Fix image regex again from alternate size methods.
Fix image regex again from alternate size methods.

The regex was matching on shopify.com in addition to the file extension.

metric-collective/shopify_python_api,gavinballard/shopify_python_api,ifnull/shopify_python_api,SmileyJames/shopify_python_api,asiviero/shopify_python_api,Shopify/shopify_python_api,varesa/shopify_python_api