resolve sympy numbers module name correctly

Sympy 1.7 broke alias `sympy.numbers` and `sympy.core.numbers` should be used
instead. Second alias, however, can't be used in eariler Sympy version. This
fix uses one of them, dependent on what attribute is present.
22 jobs for stable in 8 minutes and 26 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Build Env
manual build-env:conda #212105
allowed to fail manual
manual build-env:debian #212104
allowed to fail manual
manual build-env:default #212106
allowed to fail manual
manual build-env:ubuntu #212103
allowed to fail manual
 
  Build
passed build:debian #212108

00:02:15

passed build:latest #212111

00:01:44

passed build:no-extras #212110

00:02:06

passed build:stable #212109

00:02:12

passed build:ubuntu #212107

00:02:43

 
  Test
passed build PDF documentation #212120

00:05:19

passed build documentation #212119

00:05:07

failed check for broken links in doc #212121
allowed to fail

00:00:53

passed check for dependencies installed #212113

00:00:33

passed check whitespace style #212112

00:00:36

passed test:debian #212117

00:01:50

passed test:latest #212118

00:02:27

passed test:no-extras #212115

00:01:21

passed test:stable #212114

00:02:27

passed test:ubuntu #212116

00:01:50

 
  Deploy
manual remove_coverage #212122
allowed to fail manual
manual remove_docs #212124
allowed to fail manual
passed upload documentation to the test server #212123

00:00:21

 
Name Stage Failure
failed
check for broken links in doc Test
(     pre/install: line   35) ok        https://www.scipy.org/
(tutorial/introduction: line 28) ok https://wiki.python.org/moin/BeginnersGuide
(tutorial/first_steps: line 328) ok https://xkcd.com/353/
build finished with problems, 156 warnings.
Makefile:119: recipe for target 'linkcheck' failed
make: Leaving directory '/builds/kwant/kwant/doc'
make: *** [linkcheck] Error 1
Cleaning up file based variables
ERROR: Job failed: exit code 1