Set IDNA's CheckHyphens to the value of beStrict

It makes more sense if it's consistent with UseSTD3ASCIIRules and VerifyDnsLength.

Fixes #820.

url.bs

@@ -906,7 +906,7 @@ concepts.
  <li>
   <p>Let <var>result</var> be the result of running <a abstract-op lt=ToASCII>Unicode ToASCII</a>
   with <i>domain_name</i> set to <var>domain</var>, <i>UseSTD3ASCIIRules</i> set to
-  <var>beStrict</var>, <i>CheckHyphens</i> set to false, <i>CheckBidi</i> set to true,
+  <var>beStrict</var>, <i>CheckHyphens</i> set to <var>beStrict</var>, <i>CheckBidi</i> set to true,
   <i>CheckJoiners</i> set to true, <i>Transitional_Processing</i> set to false,
   and <i>VerifyDnsLength</i> set to <var>beStrict</var>. [[!UTS46]]
 
@@ -936,9 +936,9 @@ concepts.
 <ol>
  <li><p>Let <var>result</var> be the result of running
  <a abstract-op lt=ToUnicode>Unicode ToUnicode</a> with <i>domain_name</i> set to <var>domain</var>,
- <i>CheckHyphens</i> set to false, <i>CheckBidi</i> set to true, <i>CheckJoiners</i> set to true,
- <i>UseSTD3ASCIIRules</i> set to <var>beStrict</var>, and <i>Transitional_Processing</i> set to
- false. [[!UTS46]]
+ <i>CheckHyphens</i> set to <var>beStrict</var>, <i>CheckBidi</i> set to true, <i>CheckJoiners</i>
+ set to true, <i>UseSTD3ASCIIRules</i> set to <var>beStrict</var>, and
+ <i>Transitional_Processing</i> set to false. [[!UTS46]]
 
  <li><p>Signify <a>domain-to-Unicode</a> <a>validation errors</a> for any returned errors, and then,
  return <var>result</var>.