travis: Test only on distributions with gnuradio 3.8

Change-Id: I05706496687bff2dc4e9a111d8ecd4f878b53c12
diff --git a/.travis.yml b/.travis.yml
index f61ff6e..5230b46 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,10 +4,10 @@
 
 env:
   - DOCKERFILE=tests/dockerfiles/Debian_testing.docker IMGNAME=debtest-grgsm
-  - DOCKERFILE=tests/dockerfiles/Ubuntu_16_04.docker IMGNAME=ubu16.04-grgsm
-  - DOCKERFILE=tests/dockerfiles/Ubuntu_16_04_nolibosmo.docker IMGNAME=ubu16.04-grgsm-nolibosmo
+#  - DOCKERFILE=tests/dockerfiles/Ubuntu_16_04.docker IMGNAME=ubu16.04-grgsm
+#  - DOCKERFILE=tests/dockerfiles/Ubuntu_16_04_nolibosmo.docker IMGNAME=ubu16.04-grgsm-nolibosmo
   - DOCKERFILE=tests/dockerfiles/Kali.docker IMGNAME=kali-grgsm
-  - DOCKERFILE=tests/dockerfiles/Fedora_26.Dockerfile IMGNAME=fedora26-grgsm
+#  - DOCKERFILE=tests/dockerfiles/Fedora_26.Dockerfile IMGNAME=fedora26-grgsm
 
 
 services: