Fix link syntax in CONTRIBUTING.md (#389)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c25877c..2d9c900 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -7,7 +7,7 @@
 ## Welcome
 
 For an introduction to contributing to Flutter, see [our contributor
-guide][https://github.com/flutter/flutter/blob/master/CONTRIBUTING.md].
+guide](https://github.com/flutter/flutter/blob/master/CONTRIBUTING.md).
 
 Additional resources specific to the packages repository:
 - [Setting up the Packages development