Fix lein tasks

[nberger]

The previous fix for lein 2.5.2 introduced 2 new bugs :/

• The lein version specifier was "2.5.2-" instead of "2.5.2", so it only worked with 2.5.2-SNAPSHOT but not on 2.5.2
• For lein 2.5.1 a nil param was being passed as first argument to run, so it was interpreted as lein run, executing the main function