我正在通过pip installtravis 安装几个 python 包，
language: python
python:
- '2.7'
install:
- pip install -r requirements/env.txt
一切正常，但今天我开始收到以下错误：
Running setup.py install for cryptography
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/tmp/pip-build-hKwMR3/cryptography/setup.py", line 334, in <module>
**keywords_with_side_effects(sys.argv)
File "/opt/python/2.7.9/lib/python2.7/distutils/core.py", line 111, in setup
_setup_distribution = dist = klass(attrs)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/setuptools/dist.py", line 269, in __init__
_Distribution.__init__(self,attrs)
File "/opt/python/2.7.9/lib/python2.7/distutils/dist.py", line 287, in __init__
self.finalize_options()
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/setuptools/dist.py", line 325, in finalize_options
ep.load()(self, ep.name, value)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/setuptools_ext.py", line 181, in cffi_modules
add_cffi_module(dist, cffi_module)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/setuptools_ext.py", line 48, in add_cffi_module
execfile(build_file_name, mod_vars)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/setuptools_ext.py", line 24, in execfile
exec(code, glob, glob)
File "src/_cffi_src/build_openssl.py", line 81, in <module>
extra_link_args=extra_link_args(compiler_type()),
File "/tmp/pip-build-hKwMR3/cryptography/src/_cffi_src/utils.py", line 61, in build_ffi_for_binding
extra_link_args=extra_link_args,
File "/tmp/pip-build-hKwMR3/cryptography/src/_cffi_src/utils.py", line 70, in build_ffi
ffi.cdef(cdef_source)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/api.py", line 105, in cdef
self._cdef(csource, override=override, packed=packed)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/api.py", line 119, in _cdef
self._parser.parse(csource, override=override, **options)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 299, in parse
self._internal_parse(csource)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 304, in _internal_parse
ast, macros, csource = self._parse(csource)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 260, in _parse
ast = _get_parser().parse(csource)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 40, in _get_parser
_parser_cache = pycparser.CParser()
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/c_parser.py", line 87, in __init__
outputdir=taboutputdir)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/c_lexer.py", line 66, in build
self.lexer = lex.lex(object=self, **kwargs)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/ply/lex.py", line 911, in lex
lexobj.readtab(lextab, ldict)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/ply/lex.py", line 233, in readtab
titem.append((re.compile(pat, lextab._lexreflags | re.VERBOSE), _names_to_funcs(func_name, fdict)))
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/re.py", line 194, in compile
return _compile(pattern, flags)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/re.py", line 249, in _compile
p = sre_compile.compile(pattern, flags)
File "/home/travis/virtualenv/python2.7.9/lib/python2.7/sre_compile.py", line 583, in compile
"sorry, but this version only supports 100 named groups"
AssertionError: sorry, but this version only supports 100 named groups
解决方案？