Pin Go version to v1.18

Change-Id: I890e40d22d62303a115c098efd87de63db46c4f2
diff --git a/Dockerfile b/Dockerfile
index 312dc21..9586a6a 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM golang:latest as builder
+FROM golang:1.18 as builder
 
 ENV CGO_ENABLED=0