Alpine docker: enforce usage of Python3 (#67)

docker/Dockerfile_alpine

@@ -172,6 +172,11 @@ RUN echo "Install main packages";\
     tar xfz grass-$GRASS_VERSION.git_src_snapshot_latest.tar.gz --strip=1 -C /src/grass_build && \
     rm -f grass-$GRASS_VERSION.git_src_snapshot_latest.tar.gz; \
     #
+    # Fixup python shebangs - TODO: will be resolved in future by grass-core
+    cd /src/grass_build && \
+    find -name '*.py' | xargs sed -i 's,#!/usr/bin/env python,#!/usr/bin/env python3,' && \
+    sed -i 's,python,python3,' include/Make/Platform.make.in && \
+    #
     # Configure compile and install GRASS GIS
     #
     echo "  => Configure and compile grass";\