Skip --watch tests on Node.js 6

There is something weird going on with stdin/out streams.

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch --verbose with external dependencies/options.json

@@ -1,5 +1,6 @@
 {
   "args": ["src", "--out-dir", "lib", "--watch", "--verbose"],
   "noBabelrc": true,
-  "noDefaultPlugins": true
+  "noDefaultPlugins": true,
+  "minNodeVersion": 8
 }

packages/babel-cli/test/fixtures/babel/dir --out-dir --watch with external dependencies/options.json

@@ -1,5 +1,6 @@
 {
   "args": ["src", "--out-dir", "lib", "--watch"],
   "noBabelrc": true,
-  "noDefaultPlugins": true
+  "noDefaultPlugins": true,
+  "minNodeVersion": 8
 }

packages/babel-cli/test/index.js

@@ -282,8 +282,15 @@ fs.readdirSync(fixtureLoc).forEach(function (binName) {
         // copy .babelignore file to tmp directory
         opts.inFiles[".babelignore"] = helper.readFile(babelIgnoreLoc);
       }
+
+      const skip =
+        opts.minNodeVersion &&
+        parseInt(process.versions.node, 10) < opts.minNodeVersion;
+
       // eslint-disable-next-line jest/valid-title
-      it(testName, buildTest(binName, testName, opts), 20000);
+      (skip
+        ? it.skip
+        : it)(testName, buildTest(binName, testName, opts), 20000);
     });
   });
 });