Update Mocha to 7.1.1

None of the breaking changes listed in
https://github.com/mochajs/mocha/releases/tag/v7.0.0
appear to be relevant for us.

R=jacktfranklin@chromium.org
DISABLE_THIRD_PARTY_CHECK=Update Mocha

Bug: 1068145
Change-Id: I4aec1e775595a0cfcfaa307a8aad7fc9abad22ca
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2137392
Commit-Queue: Tim van der Lippe <tvanderlippe@chromium.org>
Reviewed-by: Jack Franklin <jacktfranklin@chromium.org>
diff --git a/node_modules/yargs-parser/lib/tokenize-arg-string.js b/node_modules/yargs-parser/lib/tokenize-arg-string.js
index 569f61a..fe05e27 100644
--- a/node_modules/yargs-parser/lib/tokenize-arg-string.js
+++ b/node_modules/yargs-parser/lib/tokenize-arg-string.js
@@ -1,6 +1,8 @@
 // take an un-split argv string and tokenize it.
 module.exports = function (argString) {
-  if (Array.isArray(argString)) return argString
+  if (Array.isArray(argString)) {
+    return argString.map(e => typeof e !== 'string' ? e + '' : e)
+  }
 
   argString = argString.trim()
 
@@ -25,7 +27,6 @@
     // don't split the string if we're in matching
     // opening or closing single and double quotes.
     if (c === opening) {
-      if (!args[i]) args[i] = ''
       opening = null
     } else if ((c === "'" || c === '"') && !opening) {
       opening = c