Allow for UTF-8 byte order mark in input files.

Fixes: #405

lib/jsduck/util/io.rb

@@ -8,13 +8,15 @@ module Util
     # have surprising results.  So in here we read in all files in UTF-8
     # (the default) or in some other encoding specified through --encoding
     # option and convert it to UTF-8 internally.
+    #
+    # We also allow for UTF-8 byte order mark.
     class IO
-      @@encoding = "UTF-8"
+      @@encoding = "BOM|UTF-8"
 
       # Sets the external encoding to be used for reading files.
       # When it's different from UTF-8, the input will be converted to UTF-8.
       def self.encoding=(e)
-        if e =~ /^UTF-8$/i
+        if e =~ /^(BOM\|)?UTF-8$/i
           @@encoding = e
         else
           @@encoding = e+":UTF-8"