Revert "⬆️ metrics@1.2.7"

This reverts commit b81e33c372.

b81e33c372 *seems* to be causing some
tests to time-out on CI:

https://circleci.com/gh/atom/atom/7707
https://circleci.com/gh/atom/atom/7708
https://circleci.com/gh/atom/atom/7709

Let's revert that change for now so that we can get CI green again while
we search for the exact cause of those time-outs.

package.json

@@ -121,7 +121,7 @@
     "line-ending-selector": "0.7.7",
     "link": "0.31.4",
     "markdown-preview": "0.159.20",
-    "metrics": "1.2.7",
+    "metrics": "1.2.6",
     "notifications": "0.70.5",
     "open-on-github": "1.3.1",
     "package-generator": "1.3.0",