Fix more-itertools breaking 2.7 & 3.5.
The 8.11.0 release today uses f-strings and old pytest floats on this
dep.
@@ -17,6 +17,9 @@ commands =
# Ensure pex's main entrypoint can be run externally.
pex --disable-cache . -e pex.bin.pex:main --version
deps =
+ # The more-itertools project is an indirect requirement of pytest and its broken for
+ # Python < 3.6 in newer releases so we force low here.
+ more-itertools<=8.10.0
pytest==4.6.11
pkginfo==1.7.0
py{27,py,py2}: mock==3.0.5
