Method#>> and Method#<< are not supported

This is supported in MRI 2.6 when proc composition was added.

```
truffleruby 19.3.0, like ruby 2.6.2, GraalVM CE Native [x86_64-darwin]
```

To reproduce:

```
$ ruby -e 'p = ->(x) { x }; def a(x); x; end; method(:a) >> p'
```

Error:

```
-e:1:in `<main>': undefined method `>>' for #<Method: Object(Object)#a -e:1>:Method (NoMethodError)
```
