Fix deprecation warning about =~ being called on TrueClass.

With the code as it was, it will generate a warning like such:

.../websocket-extensions-0.1.3/lib/websocket/extensions/parser.rb:41:
warning: deprecated Object#=~ is called on TrueClass; it always returns
nil

So we will avoid if the variable is TrueClass.

lib/websocket/extensions/parser.rb

@@ -38,7 +38,7 @@ def self.parse_header(header)
             else
               data = true
             end
-            if data =~ NUMBER
+            if data != true and data =~ NUMBER
               data = data =~ /\./ ? data.to_f : data.to_i(10)
             end