fix regexp match in yahoo lookup to use xml boundary instead of newlines....

fix regexp match in yahoo lookup to use xml boundary instead of newlines. fixes broken lookup unit test

lib/geocoder/lookups/yahoo.rb

@@ -53,7 +53,7 @@ module Geocoder::Lookup
       if raw_data.match /^<\?xml/
         if raw_data.include?("Rate Limit Exceeded")
           raise_error(Geocoder::OverQueryLimitError) || warn("Over API query limit.")
-        elsif raw_data =~ /\n(.*Please provide valid credentials.*)\n/
+        elsif raw_data =~ /<yahoo:description>(Please provide valid credentials.*)<\/yahoo:description>/i
           raise_error(Geocoder::InvalidApiKey) || warn("Invalid API key. Error response: #{$1}")
         end
       else