Fix for shebang with relative bin

`#!/usr/bin/env bin/linguist` is a valid shebang

lib/linguist/languages.yml

@@ -544,6 +544,8 @@ Crystal:
   - .cr
   ace_mode: ruby
   tm_scope: source.ruby
+  interpreters:
+  - crystal
 
 Cucumber:
   extensions:

lib/linguist/samples.rb

@@ -133,6 +133,9 @@ module Linguist
 
       script = script == 'env' ? tokens[1] : script
 
+      # If script has an invalid shebang, we might get here
+      return unless script
+
       # "python2.6" -> "python2"
       script.sub! $1, '' if script =~ /(\.\d+)$/
 
@@ -141,8 +144,8 @@ module Linguist
         lines[0...5].any? { |l| l.match(/exec (\w+).+\$0.+\$@/) }
         script = $1
       end
-
-      script
+      
+      File.basename(script)
     else
       nil
     end