title: can't use colon pair in `qqww` or `qqww:to` struct
body: <p>I want to generate a json row using a <code>Class</code>, I overwrite the <code>gist</code> method, so that it will print what I want:</p>
  
  <pre><code>my $ak = '7111ac873c9dcd5fc335ded47630d050';
  my $st = '1523451601875';
  my $ifo = 'true';
  my $uu = "15778787898988090";
  
  class Stay {
    has $.ak  is rw = '7111ac873c9dcd5fc335ded47630d050';
    has $.uu  is rw;
    has $.ifo is rw;
    has $.st  is rw;
  
    method gist() {
      #return qqww/{"ev":"app","ak":"$!ak","uu":"$!uu","ifo":"$!ifo","st":"$!st"}/;
  
      return qqww:to「EOF」;
      {"ev":"app","ak":"$!ak","uu":"$!uu","ifo":"$!ifo","st":"$!st"}
      EOF
    }
  }
  
  say Stay.new(uu =&gt; $uu, ifo =&gt; $ifo, st =&gt; $st); 
  </code></pre>
  
  <p>but fails with:</p>
  
  <pre><code>===SORRY!=== Error while compiling /Users/ohmycloud/Desktop/stay.pl6
  Confused
  at /Users/ohmycloud/Desktop/stay.pl6:18
  ------&gt;     {"ev":⏏"app","ak":"$!ak","uu":"$!uu","ifo":"$!i
      expecting any of:
          colon pair
  </code></pre>
  
  <p>What I want is:</p>
  
  <pre><code>{"ev":"app","ak":"7111ac873c9dcd5fc335ded47630d050","uu":"15778787898988090","ifo":"true","st":"1523451601875"}
  </code></pre>
  
  <p>Why I can't use colon pair in <code>qqww</code> or <code>qq:to</code> struct?</p>