Added in git checkout for the working version of graphene

graphene-docker/Dockerfile

@@ -6,6 +6,7 @@ RUN pip3 install protobuf
 WORKDIR /root
 RUN git clone https://github.com/oscarlab/graphene
 WORKDIR graphene
+RUN git checkout c0bc728
 RUN git submodule init
 RUN git submodule update
 RUN openssl genrsa -3 -out Pal/src/host/Linux-SGX/signer/enclave-key.pem 3072