Weird PostCss error in Meteor Build


Hi all,
I’ve just updated one of my projects with some new code and when I try to meteor build or push to heroku master I get this error:

Unknown error from PostCSS plugin. Your current PostCSS version is 6.0.13, but postcss-minify-selectors uses 5.2.18. Perhaps this is the source of the error below.

I am not using anything other than meteor and it gives no indication as to what specifically in my code is causing this and as such I am asking if anyone has possibly encountered a similar issue or may know the cause?