Fix thumbnails

[nkorinek]

Fixed the two vignettes that still had messed up thumbnails so that they actually point to a plot.

[nkorinek]

@lwasser this failed for a weird reason, I've never seen this error before: error: [WinError 32] The process cannot access the file because it is being used by another process: 'C:\\Users\\appveyor\\AppData\\Local\\Temp\\1\\easy_install-98pagxyi\\munch-2.3.2\\munch\\__init__.py' Command exited with code 1 Have you seen this before? Any advice? I didn't change almost anything at all, except the numbers for the vignette gallerys, so I don't think it was my code.

[codecov-io]

Codecov Report

Merging #407 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #407   +/-   ##
======================================
  Coverage    94.9%   94.9%           
======================================
  Files          25      25           
  Lines        1629    1629           
======================================
  Hits         1546    1546           
  Misses         83      83

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[lwasser]

@nkorinek sometimes appveyor is weird. i just rebuild it and it's all good!! you didn't do a thing. i've seen this before and i can't explain what happens. perhaps a file that is only isn't accessible at the moment it is trying to build??

[lwasser]

this closes #407 fix thumbnails on vignettes! thank you @nkorinek !!

[lwasser]

addresses : #381