Add IO::String dependency

Author: Altai-man

META.info

@@ -4,7 +4,7 @@
     "version"     : "*",
     "description" : "Perl 6 documentation (tools and docs)",
     "depends"     : [ "URI", "File::Temp", "JSON::Fast", "Pod::To::BigPage", "Pod::To::HTML",
-                      "OO::Monitors" ],
+                      "OO::Monitors", "IO::String" ],
     "build-depends" : [ "File::Find" ],
     "provides"    : {
         "Perl6::Type"                   : "lib/Perl6/Type.pm",