boost-python: Depends on python for Linuxbrew
boost-python: Depends on python for Linuxbrew

Fix the errors:

/usr/bin/ld: cannot find -lpython2.7

ImportError: /home/linuxbrew/.linuxbrew/lib/libboost_python.so.1.64.0:
undefined symbol: PyUnicodeUCS4_FromEncodedObject

Closes Linuxbrew/homebrew-core#2794.

Signed-off-by: Shaun Jackman <b580dab3251a9622aba3803114310c23fdb42900@gmail.com>

maxim-belkin/homebrew-core,Linuxbrew/homebrew-core,rwhogg/homebrew-core,rwhogg/homebrew-core,LinuxbrewTestBot/homebrew-core,maxim-belkin/homebrew-core,LinuxbrewTestBot/homebrew-core,Linuxbrew/homebrew-core