Add boto3 to requirements.txt

[richford]

Traceback (most recent call last):
File "bin/pyAFQ_dki", line 5, in
from AFQ import dki
File "/Users/Adam/code/projects/pyAFQ/AFQ/init.py", line 1, in
from .api import * # noqa
File "/Users/Adam/code/projects/pyAFQ/AFQ/api.py", line 15, in
import AFQ.data as afd
File "/Users/Adam/code/projects/pyAFQ/AFQ/data.py", line 5, in
import boto3
ImportError: No module named 'boto3'

conda install boto3 fixed it so I recommend adding boto3 to the requirements.txt