add python3 for mac Travis

tarzanek · tarzanek · commit 88c623c91f2b · 2019-12-20T11:40:05.000+01:00
diff --git a/dev/before_install b/dev/before_install
@@ -45,6 +45,7 @@ elif [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
 		exit 1
 	fi
 
+	brew install python3
 	brew upgrade python
 
 	./dev/install-python-packages.sh
