use release versioning

avoids problems with version pragmas and nightly versioning (which is
assumed strictly less than the equivalent release version)

Author: rainbreak

Dockerfile

@@ -19,6 +19,10 @@ RUN cd jsoncpp \
 WORKDIR /src/solidity/build
 
 RUN git checkout v0.4.2
+
+# don't use nightly versioning for releases
+RUN echo -n > ../prerelease.txt
+
 RUN cmake -DCMAKE_BUILD_TYPE=Release \
           -DTESTS=1 \
           -DSTATIC_LINKING=1 \