Convert from mode names to mimetypes for better usage.

lib/linguist/language.rb

@@ -398,13 +398,13 @@ module Linguist
     # Returns a String name or nil
     attr_reader :ace_mode
 
-    # Public: Get Codemirror mode
+    # Public: Get Codemirror mode (as expressed by a mimetype)
     #
     # Examples
     #
     #  # => "nil"
-    #  # => "javascript"
-    #  # => "clike"
+    #  # => "text/x-javascript"
+    #  # => "text/x-csrc"
     #
     # Returns a String name or nil
     attr_reader :codemirror_mode

test/test_language.rb

@@ -350,7 +350,7 @@ class TestLanguage < Minitest::Test
   end
 
   def test_codemirror_mode
-    assert_equal 'clike', Language['C++'].codemirror_mode
+    assert_equal 'text/x-c++src', Language['C++'].codemirror_mode
   end
 
   def test_wrap