docs: update links in contrib guide (#610)

CONTRIBUTING.md

@@ -16,11 +16,9 @@ Please fill out either the individual or corporate Contributor License Agreement
 (CLA).
 
   * If you are an individual writing original source code and you're sure you
-    own the intellectual property, then you'll need to sign an [individual CLA]
-    (https://developers.google.com/open-source/cla/individual).
+    own the intellectual property, then you'll need to sign an [individual CLA](https://developers.google.com/open-source/cla/individual).
   * If you work for a company that wants to allow you to contribute your work,
-    then you'll need to sign a [corporate CLA]
-    (https://developers.google.com/open-source/cla/corporate).
+    then you'll need to sign a [corporate CLA](https://developers.google.com/open-source/cla/corporate).
 
 Follow either of the two links above to access the appropriate CLA and
 instructions for how to sign and return it. Once we receive it, we'll be able to