-p results in 'invalid option' message, --precision works

[djwhitt]

Tested on master (5d39ab9):

$ ./bin/sassc --version
sassc: 3.3.0-beta1
libsass: 3.2.5
sass2scss: 1.0.3

$ git rev-parse HEAD
5d39ab99253ced0ba3b2a145611d215357332a2c

$ ./bin/sassc -p 8 < /dev/null
./bin/sassc: invalid option -- 'p'
See './bin/sassc -h'

$ ./bin/sassc --precision 8 < /dev/null
Error: Data context created with empty source string

[saper]

@djwhitt #148 should fix it, thanks for bringing this up!