Rakudo 2018.04.1

This release has lots of changes:

• bump to upstream release 2018.04.1 (2018.04 was skipped due to upstream bugs fixed on the dot release. thx to @AlexDaniel++).
• Addition of Ubuntu 18.04 amd64 and i386 packages.
• Addition of Fedora 28 x86_x64 packages.
• OS repositories for Centos 7, Debian 8 and 9, Fedora 25 and 26, openSUSE 42.3 and Ubuntu 16.04, 17.10 and 18.04. See OS Repositories.
• Repo based instructions to use rakudo-pkg on Travis.
• Script provided to set the PATH automatically .
• Support for Windows Subsystem for Linux is now included in all the packages (except Alpine).
• Better documentation.