Fix doc building on Python 2.7

12 jobs for doc27 in 16 minutes and 45 seconds (queued for 8 seconds)
Status Name Job ID Coverage
  Build
passed build_linux_27 #64895
conda-linux

00:03:37

passed build_linux_34 #64897
conda-linux

00:07:20

passed build_linux_35 #64899
conda-linux

00:04:56

passed build_macosx_27 #64900
conda-macosx

00:03:02

passed build_macosx_34 #64898
conda-macosx

00:03:49

passed build_macosx_35 #64896
conda-macosx

00:03:03

 
  Test
passed test_linux_27 #64905
conda-linux

00:02:38

69.0%
passed test_linux_34 #64903
conda-linux

00:03:55

69.0%
passed test_linux_35 #64901
conda-linux

00:03:29

69.0%
passed test_macosx_27 #64902
conda-macosx

00:04:34

69.0%
passed test_macosx_34 #64904
conda-macosx

00:04:42

69.0%
passed test_macosx_35 #64906
conda-macosx

00:04:28

69.0%