HTML Reporter: Report time as seconds in qunit-testresult-display

QUnit 2.21.0:
> 254 tests completed in 912 milliseconds, with 0 failed, 7 skipped, and 4 todo.
> 819 assertions of 823 passed, 4 failed.

New:
> 254 tests completed in 0.9 seconds, with 0 failed, 7 skipped, and 4 todo.

This is a more human-scale number. Rounding is opionated. I went with 1 digit
of precision, and thus reporting 123ms as 0.1s. For number smaller than 100ms,
I opted for a longer format with at always 1 significant digit, so reporting
20ms as 0.02s, instead of e.g. forcefully rounding either down to a confusing
0.0s or a deceptively high 0.1s. It allows for a little pride/recognition of
small numbers. As a GUI, this is not meant to be machine readable either way.
In practice, numbers below 0.1s are rare.

The `runEnd` event data is unchanged, and continues to report in milliseconds.

src/html-reporter/html.js

@@ -721,15 +721,24 @@ const stats = {
     ].join('');
   }
 
+  function msToSec (milliseconds) {
+    if (milliseconds < 1000) {
+      // Will return e.g. "0.2", "0.03" or "0.004"
+      return (milliseconds / 1000).toPrecision(1) + ' seconds';
+    }
+    const sec = Math.ceil(milliseconds / 1000);
+    return sec + (sec === 1 ? ' second' : ' seconds');
+  }
+
   QUnit.on('runEnd', function (runEnd) {
     const banner = id('qunit-banner');
     const tests = id('qunit-tests');
     const abortButton = id('qunit-abort-tests-button');
     let html = [
       runEnd.testCounts.total,
       ' tests completed in ',
-      runEnd.runtime,
-      ' milliseconds, with ',
+      msToSec(runEnd.runtime),
+      ', with ',
       runEnd.testCounts.failed,
       ' failed, ',
       runEnd.testCounts.skipped,
@@ -744,7 +753,7 @@ const stats = {
 
     // Update remaining tests to aborted
     if (abortButton && abortButton.disabled) {
-      html = 'Tests aborted after ' + runEnd.runtime + ' milliseconds.';
+      html = 'Tests aborted after ' + msToSec(runEnd.runtime) + '.';
 
       for (let i = 0; i < tests.children.length; i++) {
         test = tests.children[i];