Update apt to update ca-certs

Author: Simone Caruso

.travis.yml

@@ -4,7 +4,11 @@ language: go
 go_import_path: github.com/wavefronthq/go-metrics-wavefront
 
 before_install:
-  - sudo apt-get install --reinstall ca-certificates
+  - sudo apt-get install -y ca-certificates libgnutls30
+
+addons:
+  apt:
+    update: true
 
 go:
   - "1.11.x"