chore: upgrade go to 1.15

Signed-off-by: Bo-Yi Wu <[email protected]>

Author: appleboy

.drone.yml

@@ -6,7 +6,7 @@ clone:
 
 steps:
 - name: testing
-  image: golang:1.13
+  image: golang:1.15
   pull: true
   commands:
   - make vet
@@ -28,7 +28,7 @@ clone:
 
 steps:
 - name: testing
-  image: golang:1.13
+  image: golang:1.15
   pull: true
   commands:
   - make test