Updated tools version to 2.0.0

Also removed redundant lint-sanity (govet), and lint-style (gofmt), which are 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: Iaf53c43b0926d412f3f980dfb2d5944ff61ffb9c
diff --git a/go.mod b/go.mod
index 1719306..6d1ebba 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/opencord/voltha-openolt-adapter
 
-go 1.12
+go 1.13
 
 require (
 	github.com/EagleChen/mapmutex v0.0.0-20180418073615-e1a5ae258d8d