add an empty string handler for jest gql

Author: danielhep

__tests__/test-utils/mock-data/empty-string.js

@@ -0,0 +1 @@
+module.exports = ''

package.json

@@ -210,6 +210,7 @@
       "i18n/(.*)\\.yml$": "<rootDir>__tests__/test-utils/mock-data/empty-yml.js",
       "modeSettings.yml$": "<rootDir>__tests__/test-utils/mock-data/empty-yml.js",
       "i18n-loader": "<rootDir>__tests__/test-utils/mock-data/i18n-loader.js",
+      "\\.graphql$": "<rootDir>__tests__/test-utils/mock-data/empty-string.js",
       "\\.(jpg|ico|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>__tests__/test-utils/mock-data/fileMock.js"
     },
     "transform": {