Assigned --cacert CLI argument to correct options property

Author: Ryan Graham

bin/webpack-dev-server.js

@@ -148,7 +148,7 @@ if(argv["key"])
 	options.key = fs.readFileSync(path.resolve(argv["key"]));
 
 if(argv["cacert"])
-	options.cacert = fs.readFileSync(path.resolve(argv["cacert"]));
+	options.ca = fs.readFileSync(path.resolve(argv["cacert"]));
 
 if(argv["inline"])
 	options.inline = true;