go 1.16 features

- use go embed instead of go-binary and remove all about old assets (go 1.16 feature)
- pin gox version (go 1.16 feature)
- update ci to go 1.16

.travis.yml

@@ -11,14 +11,10 @@ addons:
   postgresql: "9.6"
 
 go:
-  - "1.12"
-  - "1.13"
-  - "1.14"
-  - "1.15"
+  - "1.16"
 
 before_install:
   - ./script/check_formatting.sh
-  - ./script/check_assets.sh
 
 install:
   - make setup
@@ -27,4 +23,4 @@ script:
   - make build
   - make test
   - make test-all
-  - make docker-release
+  - make docker-release