Update Go versions in CI config.
diff --git a/bitbucket-pipelines.yml b/bitbucket-pipelines.yml
index d4b1a14..c043207 100644
--- a/bitbucket-pipelines.yml
+++ b/bitbucket-pipelines.yml
@@ -16,14 +16,11 @@
 pipelines:
   default:  # run on each push
     - step:
-        image: golang:1.9
-        <<: *Verify
-    - step:
-        image: golang:1.10
-        <<: *Verify
-    - step:
-        image: golang:1.11
-        <<: *Verify
-    - step:
         image: golang:1.12
         <<: *Verify
+    - step:
+        image: golang:1.13
+        <<: *Verify
+    - step:
+        image: golang:1.14
+        <<: *Verify