reverted lti branch in dockerfile back to master

Dockerfile

@@ -5,7 +5,7 @@ MAINTAINER Jihane Najdi <[email protected]>
 # Default environment
 ARG RAILS_ENV='development'
 ARG ODSA_BRANCH='master'
-ARG LTI_BRANCH='textbooks'
+ARG LTI_BRANCH='master'
 
 ENV TZ=America/New_York
 RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone