Build the js-sdk in the CI script

now it's transpiled

jenkins.sh

@@ -12,6 +12,9 @@ set -x
 # install the other dependencies
 npm install
 
+# we may be using a dev branch of js-sdk in which case we need to build it
+(cd node_modules/matrix-js-sdk && npm run build)
+
 # run the mocha tests
 npm run test