Add explicit check for --watchAll=false (facebook#7433)

Resolves facebook#7180.

Author: mrmckeb

packages/react-scripts/scripts/test.js

@@ -57,7 +57,8 @@ function isInMercurialRepository() {
 // Watch unless on CI or explicitly running all tests
 if (
   !process.env.CI &&
-  argv.indexOf('--watchAll') === -1
+  argv.indexOf('--watchAll') === -1 &&
+  argv.indexOf('--watchAll=false') === -1
 ) {
   // https://github.com/facebook/create-react-app/issues/5210
   const hasSourceControl = isInGitRepository() || isInMercurialRepository();