FIX: Set TemplateFlow directory world-writeable

[effigies]

Changes proposed in this pull request

No real way to test this until merged, built and pushed to poldracklab/fmriprep:unstable to build a Singularity image off of.

Fixes #1500.

Documentation that should be reviewed

[oesteban]

Should we reset a more restrictive umask after templateflow is installed?

[effigies]

umask is local to the shell process. By my understanding, each RUN command is run in an independent shell. That's why Docker has ENV a=b instead of RUN export a=b.

[effigies]

Dockerfile:

FROM alpine:3.6

RUN umask
RUN umask 000 && umask
RUN umask

$ docker build -t umask_test .
Sending build context to Docker daemon  2.048kB
Step 1/4 : FROM alpine:3.6
 ---> 77144d8c6bdc
Step 2/4 : RUN umask
 ---> Running in 621ee0185ae2
0022
Removing intermediate container 621ee0185ae2
 ---> 4e9d5b8e4b0c
Step 3/4 : RUN umask 000 && umask
 ---> Running in b64027ef68ce
0000
Removing intermediate container b64027ef68ce
 ---> f6839a900a24
Step 4/4 : RUN umask
 ---> Running in f0e2dab2abfc
0022
Removing intermediate container f0e2dab2abfc
 ---> 9e338df90910
Successfully built 9e338df90910
Successfully tagged umask_test:latest

[effigies]

Going to merge rather than wait forever on the anatomical workflows to recache.