Merge pull request #414 from Daniel-Mietchen/patch-3

typo fix

Author: gbilder

README.md

@@ -159,7 +159,7 @@ But seriously... this is a bummer. We really want you to use the API. If you are
 
 ### Use for production services
 
-What if you want to use our API for a production service that cannot depend on the performance uncertainties of the free and open public API? What if you don't want to be affected by impolite people who do not follow the [API Etiquette](#api-etiquette) guidelines? Well, if you’re interested in using these tools or APIs for production services, we [have a service-level offering](https://www.crossref.org/services/metadata-delivery/plus-service/) called "Plus". This service provides you with with access to all supported APIs and metadata, but with extra service and support guarantees.
+What if you want to use our API for a production service that cannot depend on the performance uncertainties of the free and open public API? What if you don't want to be affected by impolite people who do not follow the [API Etiquette](#api-etiquette) guidelines? Well, if you’re interested in using these tools or APIs for production services, we [have a service-level offering](https://www.crossref.org/services/metadata-delivery/plus-service/) called "Plus". This service provides you with access to all supported APIs and metadata, but with extra service and support guarantees.
 
 #### Authorization token for Plus service