[infer][PR] Update opam version in Docker for master

Summary:
Very minor change, but uses the latest opam version available.

Please see [CONTRIBUTING.md](./CONTRIBUTING.md) for how to set up your development environment and run tests.
Pull Request resolved: https://github.com/facebook/infer/pull/1077

Differential Revision: D14703257

Pulled By: jvillard

fbshipit-source-id: 61c8dbd1e

docker/master/Dockerfile

@@ -33,7 +33,7 @@ RUN apt-get update && \
 RUN cd /usr/local/bin && ln -s /usr/bin/python2.7 python
 
 # Install opam 2
-RUN curl -sL https://github.com/ocaml/opam/releases/download/2.0.2/opam-2.0.2-x86_64-linux > /usr/bin/opam && \
+RUN curl -sL https://github.com/ocaml/opam/releases/download/2.0.3/opam-2.0.3-x86_64-linux > /usr/bin/opam && \
     chmod +x /usr/bin/opam
 
 # Disable sandboxing