Add Unity3D Metadata files as generated

lib/linguist/generated.rb

@@ -68,6 +68,7 @@ module Linguist
       generated_protocol_buffer_go? ||
       generated_protocol_buffer? ||
       generated_jni_header? ||
+      generated_unity3d_meta? ||
       vcr_cassette?
     end
 
@@ -311,5 +312,18 @@ module Linguist
       return false unless lines.count > 1
       return lines[0].include?("Generated by Cython")
     end
+
+    # Internal: Is this a metadata file from Unity3D?
+    #
+    # Unity3D Meta files start with:
+    #   fileFormatVersion: X
+    #   guid: XXXXXXXXXXXXXXX
+    #
+    # Return true or false
+    def generated_unity3d_meta?
+      return false unless extname == '.meta'
+      return false unless lines.count > 1
+      return lines[0].include?("fileFormatVersion: ")
+    end
   end
 end