Generic/LanguageConstructSpacing: fix syntax errors in the XML doc code examples

One of the invalid examples was removed because, besides containing a
syntax error, it doesn't trigger the sniff (`yieldfrom` is tokenized as
`T_STRING` and this token is not watched by the sniff). The `<code>`
title was updated to reflect the remaining examples.

Author: rodrigoprimo

src/Standards/Generic/Docs/WhiteSpace/LanguageConstructSpacingStandard.xml

@@ -29,15 +29,18 @@ $newLine;
     <code_comparison>
         <code title="Valid: Single space between yield and from.">
         <![CDATA[
-yield<em> </em>from [1, 2, 3];
+function myGenerator() {
+    yield<em> </em>from [1, 2, 3];
+}
         ]]>
         </code>
-        <code title="Invalid: No space, more than one space or newline between yield and from.">
+        <code title="Invalid: More than one space or newline between yield and from.">
         <![CDATA[
-yield<em></em>from [1, 2, 3];
-yield<em>  </em>from [1, 2, 3];
-yield<em></em>
-from [1, 2, 3];
+function myGenerator() {
+    yield<em>  </em>from [1, 2, 3];
+    yield<em></em>
+    from [1, 2, 3];
+}
         ]]>
         </code>
     </code_comparison>