Merge pull request #193 from percona/PMM-6213-remove-go-1.13

PMM-6213 Remove go 1.13 from travis.

Author: askomorokhov

.travis.yml

@@ -5,9 +5,8 @@ services:
   - docker
 
 go:
-  - 1.13.x
   - 1.14.x
-  # - TODO master
+  - tip
 
 # skip non-trunk PMM-XXXX branch builds, but still build pull requests
 branches:
@@ -18,7 +17,7 @@ go_import_path: github.com/percona/mongodb_exporter
 
 matrix:
   allow_failures:
-    - go: master
+    - go: tip
 
 stages:
   - build