Improved vim modeline detection

TLDR: This greatly increases the flexibility of vim modeline detection
to manually set the language of a file.

In vim there are two forms of modelines:

[text]{white}{vi:|vim:|ex:}[white]{options}
examples: 'vim: syntax=perl', 'ex: filetype=ruby'

-and-

[text]{white}{vi:|vim:|Vim:|ex:}[white]se[t] {options}:[text]
examples: 'vim set syntax=perl:', 'Vim: se ft=ruby:'

As you can see, there are many combinations. These changes should allow
most combinations to be used. The two most important additions are the
use of the keyword 'syntax', as well as the addition of the first form
(you now no longer need to use the keyword 'set' with a colon at the end).
The use of first form with 'syntax' is very, very common across GitHub:

https://github.com/search?l=ruby&q=vim%3A+syntax%3D&ref=searchresults&type=Code&utf8=%E2%9C%93

README.md

@@ -59,6 +59,9 @@ Alternatively, you can use Vim or Emacs style modelines to set the language for
 
 ##### Vim
 ```
+# Some examples of various styles:
+vim: syntax=java
+vim: set syntax=ruby:
 vim: set filetype=prolog:
 vim: set ft=cpp:
 ```

lib/linguist/strategy/modeline.rb

@@ -1,8 +1,19 @@
 module Linguist
   module Strategy
     class Modeline
-      EmacsModeline = /-\*-\s*(?:(?!mode)[\w-]+\s*:\s*(?:[\w+-]+)\s*;?\s*)*(?:mode\s*:)?\s*([\w+-]+)\s*(?:;\s*(?!mode)[\w-]+\s*:\s*[\w+-]+\s*)*;?\s*-\*-/i
-      VimModeline = /vim:\s*set.*\s(?:ft|filetype)=(\w+)\s?.*:/i
+      EMACS_MODELINE = /-\*-\s*(?:(?!mode)[\w-]+\s*:\s*(?:[\w+-]+)\s*;?\s*)*(?:mode\s*:)?\s*([\w+-]+)\s*(?:;\s*(?!mode)[\w-]+\s*:\s*[\w+-]+\s*)*;?\s*-\*-/i
+
+      # First form vim modeline
+      # [text]{white}{vi:|vim:|ex:}[white]{options}
+      # ex: 'vim: syntax=perl'
+      VIM_MODELINE_1 = /(?:vim|vi|ex):\s*(?:ft|filetype|syntax)=(\w+)\s?/i
+
+      # Second form vim modeline (compatible with some versions of Vi)
+      # [text]{white}{vi:|vim:|Vim:|ex:}[white]se[t] {options}:[text]
+      # ex: 'vim set syntax=perl:'
+      VIM_MODELINE_2 = /(?:vim|vi|Vim|ex):\s*se(?:t)?.*\s(?:ft|filetype|syntax)=(\w+)\s?.*:/i
+
+      MODELINES = [EMACS_MODELINE, VIM_MODELINE_1, VIM_MODELINE_2]
 
       # Public: Detects language based on Vim and Emacs modelines
       #
@@ -22,7 +33,7 @@ module Linguist
       #
       # Returns a String or nil
       def self.modeline(data)
-        match = data.match(EmacsModeline) || data.match(VimModeline)
+        match = MODELINES.map { |regex| data.match(regex) }.reject(&:nil?).first
         match[1] if match
       end
     end

test/fixtures/Data/Modelines/ruby4

@@ -0,0 +1,3 @@
+# vim: filetype=ruby
+
+# I am Ruby

test/fixtures/Data/Modelines/ruby5

@@ -0,0 +1,3 @@
+# vim: ft=ruby
+
+# I am Ruby

test/fixtures/Data/Modelines/ruby6

@@ -0,0 +1,3 @@
+# vim: syntax=Ruby
+
+# I am Ruby

test/fixtures/Data/Modelines/ruby7

@@ -0,0 +1,3 @@
+# vim: se syntax=ruby:
+
+# I am Ruby

test/fixtures/Data/Modelines/ruby8

@@ -0,0 +1,3 @@
+# vim: set syntax=ruby:
+
+# I am Ruby

test/fixtures/Data/Modelines/ruby9

@@ -0,0 +1,3 @@
+# ex: syntax=ruby
+
+# I am Ruby

test/test_modelines.rb

@@ -11,6 +11,12 @@ class TestModelines < Minitest::Test
     assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby")
     assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby2")
     assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby3")
+    assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby4")
+    assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby5")
+    assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby6")
+    assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby7")
+    assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby8")
+    assert_modeline Language["Ruby"], fixture_blob("Data/Modelines/ruby9")
     assert_modeline Language["C++"], fixture_blob("Data/Modelines/seeplusplus")
     assert_modeline Language["C++"], fixture_blob("Data/Modelines/seeplusplusEmacs1")
     assert_modeline Language["C++"], fixture_blob("Data/Modelines/seeplusplusEmacs2")