GitHub env file support (#426)

* Upgrade to the official golangci-lint action and fix some issues it found

* Update deps

* Remove a shadow warning

* Initialize the splitPattern only once

* Initial attempt at supporting $GITHUB_ENV

Needs some polishing and tests

* Now it's actually working

* Replace golang.org/x/crypto/ssh/terminal with golang.org/x/term

* Disable the issue-228 test again

* The linter is picky

* Discovered that the workflow/envs.txt had to exist in certain cases

* Fix small linter issue

.golangci.yml

@@ -1,7 +1,10 @@
+run:
+  timeout: 3m
+
 linters-settings:
   gocyclo:
     # minimal code complexity to report, 30 by default (but we recommend 10-20)
-    min-complexity: 15
+    mi-complexity: 15
   gocritic:
      disabled-checks:
       - ifElseChain