Updated tools version to 2.0.0

Also merged lint-style (gofmt) into golangci-lint (enabled gofmt).
Also removed redundant lint-sanity (govet) which is already checked by golangci-lint.
Also changed lint-mod slightly so it reverts any changes it makes go.mod, go.sum, and vendor/.

VOL-2647

Change-Id: I0da8f5db28116efaa4958dc8778ffa0e851d6640
diff --git a/go.mod b/go.mod
index 8a2410c..75d6465 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/opencord/voltha-lib-go/v3
 
-go 1.12
+go 1.13
 
 require (
 	github.com/DataDog/zstd v1.4.1 // indirect
@@ -39,7 +39,6 @@
 	golang.org/x/net v0.0.0-20190930134127-c5a3c61f89f3 // indirect
 	golang.org/x/sys v0.0.0-20191001151750-bb3f8db39f24 // indirect
 	golang.org/x/text v0.3.2 // indirect
-	google.golang.org/appengine v1.4.0 // indirect
 	google.golang.org/genproto v0.0.0-20190927181202-20e1ac93f88c // indirect
 	google.golang.org/grpc v1.24.0
 	gopkg.in/jcmturner/goidentity.v3 v3.0.0 // indirect