If the original `BUNDLE_GEMFILE` is different from the default, then the
suggestion wouldn't work as is.

Before:

```
$ util/rubocop
Could not find rubocop-1.30.1 in locally installed gems
Run `bundle install` to install missing gems.

$  rubygems git:(better-cmd-suggestion) ✗ bundle install
Could not locate Gemfile
```

After:

```
$ util/rubocop
Could not find rubocop-1.30.1 in locally installed gems
Run `bundle install --gemfile /path/to/rubygems/bundler/tool/bundler/lint_gems.rb` to install missing gems.

$ bundle install --gemfile /path/to/rubygems/bundler/tool/bundler/lint_gems.rb
Fetching gem metadata from https://rubygems.org/.........
Using ast 2.4.2
Using bundler 2.4.7
Using parser 3.1.2.0
Using rainbow 3.1.1
Using parallel 1.22.1
Using regexp_parser 2.5.0
Using rubocop-ast 1.18.0
Using rexml 3.2.5
Using ruby-progressbar 1.11.0
Using unicode-display_width 2.1.0
Fetching rubocop 1.30.1
Installing rubocop 1.30.1
Using rubocop-performance 1.14.2
Bundle complete! 2 Gemfile dependencies, 12 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.

$ util/rubocop
Inspecting 345 files
.........................................................................................................................................................................................................................................................................................................................................................

345 files inspected, no offenses detected
```

https://github.com/rubygems/rubygems/commit/bf1320d805