stop shipping files end-users do not need

[grosser]

more of a test-balloon PR for adding the Gemfile, because that made rake fail too ... how do you suggest fixing the test failure ? @drbrain

--- Manifest.txt	2019-05-07 01:13:22.747033068 +0000
+++ Manifest.tmp	2019-05-07 01:13:55.529703866 +0000
@@ -1,6 +1,13 @@
+.autotest
+.gemtest
+.travis.yml

[drbrain]

This saves ~25K on disk and ~7K in the gem, it's not worth the maintenance burden going forward given 1GB of gp2 EBS costs $0.10/month, around $3.2e−05/month