Describe the bug A clear and concise description of what the bug is.

Running black in the console generates a traceback.

To Reproduce Steps to reproduce the behavior:
Running black directly in the console gives me the following traceback.

Traceback (most recent call last):
  File "/Users/jonathan/projects/recorded/integrations/splunk/venv/bin/black", line 7, in <module>

#4478 included some initial support for the new ConstBlock expression kind variant, but there's opportunities to enhance and improve the formatting.

The relevant section of the codebase can be found in formatting/expr.rs
https://github.com/rust-lang/rustfmt/blob/cbe01e47024c852e2ed852671e76f7929c4bab91/src/formatting/expr.rs#L127-L129

There are 3 core activities to completing this issue:

When I try to beautify the i get the following problem
TypeError: Cannot read property 'on' of undefined

I just installed beautify and uncrustify

https://gist.github.com/ODCA117/917affd6b11437517535a45350379820

We need to update our README.md file before the 1.0 release.