[travis] force protobuf 3.0.0b2 for Python 3

This is temporary measure to avoid an apparent upstream issue with
protobuf 3.0.0b2.post1.

diff --git a/scripts/travis/travis_install.sh b/scripts/travis/travis_install.sh
index d18dc22..ca8c410 100755 (executable)
--- a/scripts/travis/travis_install.sh
+++ b/scripts/travis/travis_install.sh
@@ -93,7 +93,7 @@ if [ "$PYTHON_VERSION" -eq "3" ] && [ ! -e "$CONDA_DIR/bin/protoc" ]; then
 fi
 
 if [ "$PYTHON_VERSION" -eq "3" ]; then
-  pip install --pre protobuf
+  pip install --pre protobuf==3.0.0b2
 else
   pip install protobuf
 fi