travis: remove tip and add 1.9

Author: mcuadros

.travis.yml

@@ -2,7 +2,7 @@ language: go
 
 go:
   - 1.8
-  - tip
+  - 1.9
 
 go_import_path: gopkg.in/src-d/go-git.v4
 
@@ -11,11 +11,6 @@ env:
   - GIT_VERSION=v1.9.3
   - GIT_VERSION=v2.11.0
 
-matrix:
-  fast_finish: true
-  allow_failures:
-    - go: tip
-
 cache:
   directories:
   - $HOME/.git-dist
@@ -48,4 +43,4 @@ script:
   - go vet ./...
 
 after_success:
-  - bash <(curl -s https://codecov.io/bash)
+  - bash <(curl -s https://codecov.io/bash)