This was introduced in 5074707. Since then travis fails to build; it
says "missing config".[1]
Unfortunately the travis validation at http://lint.travis-ci.org/
is out of date; it doesn't even know about the "file" option, nor
"addons", "notifications", etc.
According to the comment on this stackoverflow answer[2] the "file_glob"
option existed at some point but now has been removed, and it is
implied.
I've also removed "branch: master" to avoid confusion, because "tags:
true" (added in 5074707) causes the "branch" condition to be
ignored.[3]
[1]: https://travis-ci.org/OpenHantek/openhantek/requests
[2]: http://stackoverflow.com/a/28579635/606705
[3]: https://docs.travis-ci.com/user/deployment/#Conditional-Releases-with-on%3A
