pin the checkout of galaxy

Dockerfile

@@ -12,7 +12,7 @@ RUN apt-get update && apt-get install -y \
   curl \ 
   libpq-dev \
   vim
-RUN git clone --depth 1 --progress https://github.com/common-workflow-language/galaxy.git /app/galaxy
+RUN git clone --depth 1 --single-branch --branch cwl-1.0-prerebase-20190626 --progress https://github.com/common-workflow-language/galaxy.git /app/galaxy
 RUN git clone --depth 1 --single-branch --branch master --progress https://github.com/EBI-metagenomics/workflow-is-cwl /app/workflow-is-cwl
 RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
 RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list