Ignore files when exporting package

This commit is part of a campaign to reduce the amount of data transferred to save global bandwidth and reduce the amount of CO2. See Codeception/Codeception#5527 for more info.

Author: simonschaufi

.gitattributes

@@ -0,0 +1,6 @@
+/doc export-ignore
+/features export-ignore
+/spec export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore
+/.travis.yml export-ignore