Update String reference to match WHATWG infra spec

The Infra Spec has started calling JavaScript Strings Strings in whatwg/infra#292 and this aligns the webdriver spec with that.

Author: AutomatedTester

index.html

@@ -5835,8 +5835,8 @@ <h4><dfn>Element Send Keys</dfn></h4>
  <dd>
  <ol>
  <li><p>If <var>element</var> does not currently have focus, 
- let <var>current text length</var> be the <a>JavaScript
- string’s length</a> of <var><a>element</a></var>’s <a>API value</a>.
+ let <var>current text length</var> be the
+ <a>string length</a> of <var><a>element</a></var>’s <a>API value</a>.
 
  <li><p>Set the text insertion caret using <a>set selection range</a>
  using <var>current text length</var> for both the <code>start</code>
@@ -9910,7 +9910,7 @@ <h2>Index</h2>
  in the Infra standard: [[INFRA]]
  <ul>
  <!-- ASCII lowercase --> <li><dfn data-lt="lowercase"><a href=https://infra.spec.whatwg.org/#ascii-lowercase>ASCII lowercase</a></dfn>
- <!-- Javascript String's length --> <li><dfn><a href="https://infra.spec.whatwg.org/#javascript-string-length">JavaScript string’s length</a></dfn>
+ <!-- string length --> <li><dfn><a href="https://infra.spec.whatwg.org/#string-length">string length</a></dfn>
  <!-- queue --> <li><dfn><a href=https://infra.spec.whatwg.org/#queues>queue</a></dfn>
  <!-- set --> <li><dfn><a href=https://infra.spec.whatwg.org/#sets>Set</a></dfn>
  </ul>