go.mod: bump to Go 1.17

Author: mhagger

go.mod

@@ -1,6 +1,6 @@
 module github.com/github/git-sizer
 
-go 1.16
+go 1.17
 
 require (
 	github.com/cli/safeexec v1.0.0
@@ -10,3 +10,8 @@ require (
 	go.uber.org/goleak v1.1.12
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
 )
+
+require (
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c // indirect
+)