nginx: fix passenger detection and module location

--root changed to an ini file but the check was looking for a directory

Change to ini file:
https://github.com/Homebrew/homebrew/commit/647bc623eeead6aa65e363f9eb217f2d22dd1954#diff-4c5ad3632359bced787cfdf4d12e50b2R46
https://github.com/Homebrew/homebrew/commit/c6ed5700d81330c7fc9e2782f37fda26d3d5fefb