added update_offline in makefile to update plotlyjs

Author: yankev

makefile

@@ -57,3 +57,16 @@ pull_chunked : submodules/chunked_requests
 	@echo ""
 	@echo "Pulling down updates from chunked_requests"
 	cd submodules/chunked_requests; git pull origin master
+
+update_offline :
+	@echo "Updating plotly.js"
+	@echo "------------------"
+	python -c "import urllib2;\
+						 cdn_url = 'https://cdn.plot.ly/plotly-latest.min.js';\
+						 response = urllib2.urlopen(cdn_url);\
+						 html = response.read();\
+						 f = open('./plotly/offline/plotly.min.js', 'w');\
+    		 		 f.write(html);\
+						 f.close()"
+	@echo ""
+	@echo "Remember to update the CHANGELOG!"