Dockerfile for building Telegram Desktop (telegramdesktop/tdesktop#3978)

[vhborges]

No description provided.

[CLAassistant]

All committers have signed the CLA.

[vhborges]

Seems like travis is blocking my pull request. This is my first contribution so I didn't know about it until now, sorry.
Maybe this file would do the job? My commit has the one included on develop branch.

[auchri]

@vhborges

Error response from daemon: Dockerfile parse error line 32: unknown instruction: FI

[vhborges]

Fixed.

One thing I forgot to mention before is that the breakpad build from the tdesktop build instructions was producing an error regarding "gmock" and "gtest" but I couldn't find a safe way to fix it, plus the generated binary is working fine in my tests, so I decided to put an "exit 0" at the end of the correspondent RUN instruction. If there's a problem on this please let me know.

[auchri]

I think that this should be reworked, since Travis CI allows to share the cache between jobs... like I triad in my branch here: https://github.com/telegramdesktop/docker_linux_build/blob/auchri-patch-1/.travis.yml

travis-ci/travis-ci#7590 (comment)

[vhborges]

Unfortunately my recent schedules don't let me work on this anymore, manly because I don't have much knowledge on how Travis works. I saw that this fork is apparently continuing my work, if it's not done by December I can get back to it.