Use linebreaks in passenv list in tox.ini
@@ -19,7 +19,16 @@ indexserver =
setenv = MPLBACKEND=agg
# Pass through the following environment variables which may be needed for the CI
-passenv = HOME WINDIR LC_ALL LC_CTYPE CC CI TRAVIS GAMMAPY_DATA PKG_CONFIG_PATH
+passenv =
+ HOME
+ WINDIR
+ LC_ALL
+ LC_CTYPE
+ CC
+ CI
+ TRAVIS
+ GAMMAPY_DATA
+ PKG_CONFIG_PATH
# Run the tests in a temporary directory to make sure that we don't import
# this package from the source tree
