Capitalize error string

Author: sbscully

lib/opencage/geocoder.rb

@@ -13,7 +13,7 @@ def initialize(default_options = {})
     end
 
     def geocode(location, options = {})
-      raise_error("400 not a valid location: `#{location.inspect}`") unless location.is_a?(String)
+      raise_error("400 Not a valid location: `#{location.inspect}`") unless location.is_a?(String)
 
       request = Request.new(@api_key, location, options)