Add detection for .yaml and .yml

PR-URL: #717
Credit: @jsumners
Close: #717
Reviewed-by: @isaacs

EDIT(@isaacs): clean up test somewhat to use t.testdir() instead of
manually creating and removing files.

bin/run.js

@@ -826,7 +826,16 @@ const parseRcFile = path => {
   let contents
   try {
     contents = fs.readFileSync(path, 'utf8')
-  } catch (er) {
+  } catch (_) {
+    try {
+      contents = fs.readFileSync(path + '.yaml', 'utf8')
+    } catch (_) {
+      try {
+        contents = fs.readFileSync(path + '.yml', 'utf8')
+      } catch (_) {}
+    }
+  }
+  if (!contents) {
     // if no dotfile exists, just return an empty object
     return {}
   }

test/run/rcfile-extensions.js

@@ -0,0 +1,27 @@
+const {
+  run,
+  dir,
+  t,
+} = require('./')
+
+const fs = require('fs')
+t.test('finds rc file with .yaml and .yml', t => {
+  const files = [
+    '.taprc',
+    '.taprc.yml',
+    '.taprc.yaml',
+  ]
+
+  t.plan(files.length)
+  for (const file of files) {
+    t.test(file, t => {
+      const cwd = t.testdir({
+        [file]: 'check-coverage: false',
+      })
+      run(['--dump-config'], { cwd }, (er, o, e) => {
+        t.match(o, /check-coverage: false/)
+        t.end()
+      })
+    })
+  }
+})