Auto merge of rust-lang#3681 - rmcteggart-r7:master, r=matthiaskrgr

Fixing typo in CONTRIBUTING.md

Noticed small typo in CONTRIBUTING readme when working on another issue

CONTRIBUTING.md

@@ -79,7 +79,7 @@ to lint-writing, though it does get into advanced stuff. Most lints consist of a
 of this.
 
 If you want to add a new lint or change existing ones apart from bugfixing, it's
-also a good idea to give the [stability guaratees][rfc_stability] and
+also a good idea to give the [stability guarantees][rfc_stability] and
 [lint categories][rfc_lint_cats] sections of the [Clippy 1.0 RFC][clippy_rfc] a
 quick read.