Add docker for integration tests (#26)

tests/Dockerfile

@@ -0,0 +1,36 @@
+FROM rust:latest
+
+# Install Node.js
+ENV NODE_VERSION 12.0.0
+RUN curl https://raw.githubusercontent.com/creationix/nvm/master/install.sh | bash \
+  && . $HOME/.nvm/nvm.sh \
+  && nvm install $NODE_VERSION \
+  && nvm alias default $NODE_VERSION \
+  && nvm use default
+ENV PATH /root/.nvm/versions/node/v$NODE_VERSION/bin:$PATH
+# Check that Node.js was correctly installed
+RUN node --version 
+
+# Create blank project
+RUN USER=root cargo new --bin starship
+WORKDIR /starship
+
+# We want dependencies cached, so copy those first
+COPY ./Cargo.lock ./Cargo.lock 
+COPY ./Cargo.toml ./Cargo.toml 
+
+# Cargo.toml will fail to parse without my_benchmark
+RUN mkdir benches
+RUN touch benches/my_benchmark.rs
+
+# This is a dummy build to get dependencies cached
+RUN cargo build --release
+
+# Delete the dummy build
+RUN rm -rf /starship
+
+# Create the directory for the real source files
+RUN mkdir starship
+WORKDIR /starship
+
+CMD [ "cargo", "test", "--", "--ignored"]