fixed grammar

(cherry picked from commit ecfdca2f15d839deedcf9db47971d79e1f340e1e)

fix elastic#666

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 _Elasticsearch is an open source project and we love to receive contributions from our community — you! There are many ways to contribute, from writing tutorials or blog posts, improving the documentation, submitting bug reports and feature requests or writing code which can be incorporated into Elasticsearch itself._
 
-Please read the [contributing guidelines][] which explains in detail how contribute to Elasticsearch. The _short_ version is given below:
+Please read the [contributing guidelines][] which explain in detail how to contribute to Elasticsearch. The _short_ version is given below:
 
 # For questions, please use the forum not the issue tracker
 
@@ -42,4 +42,4 @@ Then sit back and wait. There will probably be discussion about the pull request
 [contributing guidelines]: http://www.elasticsearch.org/contributing-to-elasticsearch/
 [Contributor License Agreement]: http://www.elasticsearch.org/contributor-agreement/
 [submit a pull request]: http://help.github.com/articles/using-pull-requests
-[find or open an issue]: http://github.com/elasticsearch/elasticsearch-hadoop/issues
+[find or open an issue]: http://github.com/elasticsearch/elasticsearch-hadoop/issues