`--check [FILE]` returns `0` exit code for invalid syntax

[reese]

• Rubyfmt git sha: e00d2ab89fd4b0b85a7897fac393c1ad987136de (0.10.0)

Input file + Rubyfmt's output

$ cat hi.rb
bad syntax in here

$ cat hi.rb | cargo run -- --check
Rubyfmt detected a syntax error in the ruby code being executed

$ echo $?
1

$ cargo run -- --check hi.rb 
Rubyfmt detected a syntax error in the ruby code being executed

$ echo $?
0

This breaks because

These two are inconsistent (despite having the same input), and realistically it should probably return 5 in both cases (since we return 5 for invalid syntax in normal runs).