cosa: bump Go to 1.17

Earlier versions are EOL.

Author: bgilbert

go.mod

@@ -1,5 +1,10 @@
 module github.com/coreos/coreos-assembler
 
-go 1.15
+go 1.17
 
 require github.com/spf13/cobra v1.5.0
+
+require (
+	github.com/inconshreveable/mousetrap v1.0.0 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+)

vendor/github.com/spf13/cobra/go.mod

@@ -1,7 +1,9 @@
 # github.com/inconshreveable/mousetrap v1.0.0
+## explicit
 github.com/inconshreveable/mousetrap
 # github.com/spf13/cobra v1.5.0
-## explicit
+## explicit; go 1.15
 github.com/spf13/cobra
 # github.com/spf13/pflag v1.0.5
+## explicit; go 1.12
 github.com/spf13/pflag