[xdl] don't log dots when downloading gradle

[dsokal]

Why

From expo/turtle#221:

When running turtle build:android the logger outputs a lot of dots, which introduces noise for later analysis

How

I added a logger line transformer which drops lines that only contain dots.

Test Plan

• I yarn-linked @expo/xdl in my local turtle-cli repository.
• I ran an Android build and verified that no dots are displayed when Gradle Wrapper is downloading the appropriate Gradle version:

[brentvatne]

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nice