FIX: Use raw strings to fix escape characters; MNT: Avoid numpy.testing deprecation warning

[larsoner]

Fixes a couple of escape char problems, and a NumPy import that is deprecated in 1.15 leading to:

DeprecationWarning: Importing from numpy.testing.decorators is deprecated since numpy 1.15.0, import from numpy.testing instead.

I still need to ping the NumPy people to see if the workaround for skipif is the correct one, so WIP for now.

[coveralls]

Coverage decreased (-0.01%) to 91.812% when pulling cf76f6e on larsoner:fixes into d45417a on nipy:master.

[effigies]

@larsoner Let us know if you want a review. I'm assuming we're still waiting on confirmation from numpy folks.

[larsoner]

@effigies it should be okay, I think it's the correct fixed. Title updated

[effigies]

Cool. Want to merge master to get the tests working again?

[codecov-io]

Codecov Report

Merging #705 into master will increase coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #705      +/-   ##
==========================================
+ Coverage   88.84%   88.86%   +0.02%     
==========================================
  Files          93       93              
  Lines       11464    11453      -11     
  Branches     1896     1892       -4     
==========================================
- Hits        10185    10178       -7     
+ Misses        937      935       -2     
+ Partials      342      340       -2

Impacted Files	Coverage Δ
nibabel/affines.py	100% <ø> (ø)	⬆️
nibabel/info.py	100% <100%> (ø)	⬆️
nibabel/testing/__init__.py	94% <60%> (-1.84%)	⬇️
nibabel/cifti2/cifti2.py	96.36% <0%> (-0.03%)	⬇️
nibabel/streamlines/trk.py	94.29% <0%> (-0.02%)	⬇️
nibabel/streamlines/tck.py	98.89% <0%> (-0.02%)	⬇️
nibabel/volumeutils.py	92.78% <0%> (+0.02%)	⬆️
nibabel/openers.py	76.47% <0%> (+0.66%)	⬆️
nibabel/viewers.py	96.66% <0%> (+1.25%)	⬆️

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