fix warning: add os

Vladimir Kotal · Vladimir Kotal · commit 70099a6a805a · 2020-09-30T08:39:44.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,3 +1,4 @@
+os: linux
 dist: trusty
 before_install:
 - sudo apt-get -qq update && sudo apt-get install -y --no-install-recommends texlive-fonts-recommended

Original file line number	Diff line number	Diff line change
`@@ -1,3 +1,4 @@`
	`1`	`+os: linux`
`1`	`2`	`dist: trusty`
`2`	`3`	`before_install:`
`3`	`4`	`- sudo apt-get -qq update && sudo apt-get install -y --no-install-recommends texlive-fonts-recommended`