don't install optional dependencies when testing on pypy3 since 'blac…

…k' depends on 'typed_ast' which isn't supported on pypy3

test_versions

@@ -73,6 +73,12 @@ for PYTHON_VERSION in ${PYTHON_VERSIONS} ; do
         exit 7
     fi
     hash -r
+    REQUIREMENTS_FILE="requirements-optional.txt"
+    if [ "${PYTHON}" == "pypy3" ] ; then
+        # `black` depends on `typed_ast` which isn't supported by pypy3. We can remove this once
+        # `black` starts depending on built-in `ast`
+        REQUIREMENTS_FILE="requirements.txt"
+    fi
     ${VENV_DIR}/bin/pip install -r requirements-optional.txt | grep -Ev "Requirement already|however version|consider upgrading"
     deactivate
 done