hostsfile: lower module Go version to 1.17

Set the module directive to Go 1.17, which is the oldest version
that still compiles the repository because the code uses os.CreateTemp.

Run the standard formatting and fix-up commands and verify the package
tests pass under both the current toolchain and Go 1.17. No go.sum file
is generated because the repository has no external module dependencies.

Author: burkebot

go.mod

@@ -1,3 +1,3 @@
 module github.com/kevinburke/hostsfile
 
-go 1.24.0
+go 1.17