fix: Typo stager -> assert_cmd

EverlastingBugstopper · EverlastingBugstopper · commit 438c3481f5f5 · 2020-10-07T15:07:28.000-05:00
it looks like CONTRIBUTING.md was copied from [stager](https://github.com/crate-ci/stager) and the name was just never updated
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
@@ -1,4 +1,4 @@
-# Contributing to stager
+# Contributing to assert_cmd
 
 Thanks for wanting to contribute! There are many ways to contribute and we
 appreciate any level you're willing to do.

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-# Contributing to stager`
	`1`	`+# Contributing to assert_cmd`
`2`	`2`
`3`	`3`	`Thanks for wanting to contribute! There are many ways to contribute and we`
`4`	`4`	`appreciate any level you're willing to do.`