ruby-build 20200722
* Fix a bash 4.4 warning when installing jruby
In particular, the following:
```
/path/to/bin/ruby-build: line 739: warning: command substitution: ignored null byte in input
```
* add mruby 2.1.1
* Added rbx-4.16 to 5.0
* compatible with macOS 11
* Add definition for JRuby 9.2.12.0
https://www.jruby.org/2020/07/01/jruby-9-2-12-0.html
* Add support for installing GraalVM
* Supports using other GraalVM languages such as JavaScript, Python, R and Java.
* Supports running TruffleRuby on JVM and not only Native.
* Add GraalVM 20.1.0.
* Rename definition to truffleruby+graalvm
* '+' needs to be considered part of the name for --definitions and -l
to see truffleruby and truffleruby+graalvm as separate.