Merge branch 'release-3.1.1' into 'master'

Change the version number to 3.1.1

See merge request !46
6 jobs for 3.1.1 in 2 minutes and 53 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #35466422
docs

00:01:16

passed #35466421
lint

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passed #35466417
python2.7

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passed #35466418
python3.4

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passed #35466419
python3.5

00:01:31

passed #35466420
python3.6

00:01:49