Improvement: don't parse update response

The result of an update is not accessible to the caller. Therefore,
there is no point of parsing it and it's a risk that the whole call
fails if an error occurs during the parsing.

Fixes #71

(cherry picked from commit 3f21267)

Author: cecton

lib/sparql/client.rb

@@ -324,7 +324,7 @@ def update(query, options = {})
         require 'sparql' unless defined?(::SPARQL::Grammar)
         SPARQL.execute(query, @url, options.merge(update: true))
       else
-        parse_response(response(query, options), options)
+        response(query, options)
       end
       self
     end