[en] Try to improve MANY_NN for #1877

@danielnaber , the term '18-year-olds' has the postag NNS.
correction="many 18-year-olds" should work, but it doesn't.
Any ideas why?

languagetool-language-modules/en/src/main/resources/org/languagetool/rules/en/grammar.xml

@@ -17130,6 +17130,7 @@ USA
             <example>I have <marker>many books</marker>.</example>
             <example>I have <marker>much wine</marker>.</example>
             <example correction="many ways">... which is right in <marker>many way</marker>.</example>
+            <example correction="many ">How <marker>many 18-year-old</marker> are coming?</example><!-- #1877. Why can't I use correction="many 18-year-olds" ? -->
             <example>The state legislature gerrymandered the few Birmingham legislative seats.</example>
             <example>A few work as technical writers, others don't.</example>
 <!-- False negative --><example><marker>Many cares</marker> for her.</example><!-- Refer to http://forum.languagetool.org/t/en-false-positive-aggreement-error/1210 -->