[YUNIKORN-819] Update go version dependency to 1.15 (#54)

diff --git a/go.mod b/go.mod
index 1d109b6..8b7bec7 100644
--- a/go.mod
+++ b/go.mod
@@ -19,7 +19,7 @@
 
 module github.com/apache/incubator-yunikorn-scheduler-interface
 
-go 1.12
+go 1.15
 
 require (
 	google.golang.org/grpc v1.26.0