minor comment change

lib/fakefs/file.rb

@@ -398,7 +398,7 @@ module FakeFS
       (@mode & mask) != 0 if @mode.is_a?(Integer)
     end
 
-    # Create a missing file if the path's valid.
+    # Create a missing file if the path is valid.
     #
     def create_missing_file
       raise Errno::EISDIR, "Is a directory - #{path}" if File.directory?(@path)