use double quotes around pkgs in conda and pip installs

[kaczmarj]

related to nipy/nipype#2963 (comment)

[codecov-io]

Codecov Report

Merging #287 into master will increase coverage by 0.76%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #287      +/-   ##
==========================================
+ Coverage   80.86%   81.63%   +0.76%     
==========================================
  Files          33       33              
  Lines        1568     1568              
  Branches      170      170              
==========================================
+ Hits         1268     1280      +12     
+ Misses        219      207      -12     
  Partials       81       81

Impacted Files	Coverage Δ
neurodocker/interfaces/tests/test_miniconda.py	100% <ø> (ø)	⬆️
neurodocker/generators/singularity.py	75.57% <0%> (+0.76%)	⬆️
neurodocker/interfaces/tests/utils.py	72.41% <0%> (+12.64%)	⬆️

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