Filter out internal commits from the changelog

[TheSavior]

Facebook employees have been tagging their commits with [Internal] in order to remove them from the changelog. This wasn't being picked up by the changelog generator. This is an example commit that wasn't being filtered: https://github.com/facebook/react-native/commit/40ee0ad

The commit summary is:

LogBox - Re-apply badge color fix

Summary:
The previous diff mistakenly landed an old version

Changelog: [Internal]

The script was only looking for [Internal] in LogBox - Re-apply badge color fix. Now it looks for it on any line.

Before this change:

$ yarn generate -b 8c7ec519812c570535912c45dd81db51ba2fdd31 -c bdd1a675ba6949868d11ef0c3dccaa8f336ca384 | wc -l
284

After:

$ yarn generate -b 8c7ec519812c570535912c45dd81db51ba2fdd31 -c bdd1a675ba6949868d11ef0c3dccaa8f336ca384 | wc -l
154