Drop support for Go < 1.19.

Certain core library features such as atomic int64, any, tls
NetConn and other minute detail things that our dependencies
now rely on are entirely missing from older Go version. Since I do
not like to run downgrades, drop the older Go versions instead.

.github/workflows/go.yml

@@ -11,8 +11,6 @@ jobs:
     strategy:
       matrix:
         goversion:
-          - '1.17'
-          - '1.18'
           - '1.19'
           - '1.20'
           - '1.21'

go.mod

@@ -1,6 +1,6 @@
 module github.com/icedream/go-stagelinq
 
-go 1.17
+go 1.19
 
 require (
 	github.com/stretchr/testify v1.9.0