gdal failure builds/77217684

https://travis-ci.org/OSGeo/gdal/builds/77217684

Running tests from alg/contour.py
  TEST: contour_1 ... success
  TEST: contour_2 ... success
  TEST: contour_cleanup ... success
... failed to load gnm_test.py ... skipping.
Traceback (most recent call last):
  File "pymod/gdaltest.py", line 233, in run_all
    exec("import " + module)
  File "<string>", line 1, in <module>
  File "./gnm_test.py", line 43, in <module>
  File "/usr/local/lib/python2.7/dist-packages/GDAL-2.1.0-py2.7-linux-x86_64.egg/osgeo/gnm.py", line 28, in <module>
    _gnm = swig_import_helper()
  File "/usr/local/lib/python2.7/dist-packages/GDAL-2.1.0-py2.7-linux-x86_64.egg/osgeo/gnm.py", line 24, in swig_import_helper
    _mod = imp.load_module('_gnm', fp, pathname, description)
ImportError: /usr/local/lib/python2.7/dist-packages/GDAL-2.1.0-py2.7-linux-x86_64.egg/osgeo/_gnm.so: undefined symbol: _ZTI10GNMNetwork
Running tests from utilities/test_ogrtindex.py
  TEST: test_ogrtindex_1 ... success
  TEST: test_ogrtindex_2 ... success
  TEST: test_ogrtindex_cleanup ... success