ensure releases uses GH_TOKEN to fetch data

Currently the releases task is failing on travis because the tokenless
request has hit the rate limit. Adding the Authorization header to add
the token should lift the rate limit to much higher, and as such the
request will succeed - fixing the build!

Author: keithamus

Makefile

@@ -32,7 +32,7 @@ chaijs: ./node_modules/chai/chai.js
 
 releases: clean-releases
 	@mkdir -p _data
-	@curl -s "https://api.github.com/repos/chaijs/chai/releases" > _data/releases.json
+	@curl -s $(shell [ -n "${GH_TOKEN}" ] && echo "-H \"Authorization: token ${GH_TOKEN}\"") "https://api.github.com/repos/chaijs/chai/releases" > _data/releases.json
 
 #
 # Generate plugins