potential fix for YAMLish, but it's ugly

YAMLish.diff

diff --git a/lib/YAMLish.pm6 b/lib/YAMLish.pm6
index 0848ed4..ca200ce 100644
--- a/lib/YAMLish.pm6
+++ b/lib/YAMLish.pm6
@@ -451,7 +451,11 @@ grammar Grammar {
                        make ~$/;
                }
                method single-quoted($/) {
-                       make $<value>.Str.subst(/<Grammar::foldable-whitespace>/, ' ', :g).subst("''", "'", :g);
+                       my $value = $<value>.Str;
+                       make do {
+                               my $/;
+                               $value.subst(/<Grammar::foldable-whitespace>/, ' ', :g).subst("''", "'", :g);
+                       }
                }
                method single-key($/) {
                        make $<value>.Str.subst("''", "'", :g);