fix typo in CONTRIBUTING.rst

Author: chuangw6

CONTRIBUTING.rst

@@ -11,7 +11,7 @@ Contributor Agreement
 ----------------------
 
 By contributing,
-you agree that we may redistribute your work under our license].
+you agree that we may redistribute your work under our license.
 In exchange,
 we will address your issues and/or assess your change proposal as promptly as 
 we can, and help you become a member of our community.