Bug report

When using the baseline error format (to generate a baseline file to include to ignore legacy errors), it appears that < is not getting escaped properly.

Here's an example of one that was put in my baseline file (using PHPStan 0.12.4):

message: "#^Comparison operation \"\<\\=\" between \\*NEVER\\* and 5 is always true\\.$#"

Here's a similar error added, but with > instead of <:

message: "#^Comparison operation \"\\>\\=\" between \\*NEVER\\* and 1 is always true\\.$#"

Notice that > is getting two escaping slashes before it but < only gets one.

This seems to happen whenever < is encountered, not just on this particular message.

When trying to include the baseline file, PHPStan throws an exception:

In Decoder.php line 331:
Invalid escaping sequence < on line 64, column 13.

If I manually add the additional escape slash, the file parses fine.