[travis] Lower versions of Debian and Fedora

This should reduce general bugginess, and works around immediate
issues with both.

Signed-off-by: Robbie Harwood <rharwood@redhat.com>

Author: frozencemetery

.travis.yml

@@ -7,9 +7,9 @@ services:
   - docker
 
 env:
-  - DISTRO=fedora:rawhide COMPILER=gcc
-  - DISTRO=fedora:rawhide COMPILER=clang
-  - DISTRO=debian:sid COMPILER=clang
+  - DISTRO=fedora:27 COMPILER=gcc
+  - DISTRO=fedora:27 COMPILER=clang
+  - DISTRO=debian:testing COMPILER=clang
 
 script:
   - >