Updated exec command args to work with ST2 and ST3.

[RoccoC]

When using the Haxe Bundle with ST2, running a build throws an error due to invalid arguments getting passed to the ST exec command. ST2 does not support the "syntax" argument, and so the command execution fails. Updated the run_command() logic to only pass the syntax arg if running ST3+.

[RoccoC]

Note: See here for valid ST2 exec args, and here for valid ST3 exec args (unofficial documentation).

[ghost]

Thanks.