Switch to "usetesting" linter (#400)

Author: sethvargo

.golangci.yml

@@ -74,11 +74,11 @@ linters:
     - 'sqlclosecheck'
     - 'staticcheck'
     - 'stylecheck'
-    - 'tenv'
     - 'thelper'
     - 'typecheck'
     - 'unconvert'
     - 'unused'
+    - 'usetesting'
     - 'wastedassign'
     - 'whitespace'
     - 'wrapcheck'
@@ -178,6 +178,10 @@ linters-settings:
     # default: false
     args-on-sep-lines: true
 
+  usetesting:
+    # default: false
+    os-temp-dir: true
+
   wrapcheck:
     ignoreSigRegexps:
       - '\.ErrorOrNil\('