tox: Gevent no longer fails to install with python2-dbg

https://github.com/gevent/gevent/issues/1461 was fixed in
https://github.com/gevent/gevent/commit/cc7e28cf

tox.ini

 [tox]
 envlist =
-    {      py27,py36,py37d,py37,pypy,pypy3}-{thread,gevent}
-# XXX gevent fails to install with python2-dbg (https://github.com/gevent/gevent/issues/1461)
-    {py27d                                }-{thread       }
+    {py27d,py27,py36,py37d,py37,pypy,pypy3}-{thread,gevent}
 
 
 # ThreadSanitizer
@@ -12,14 +10,12 @@ envlist =
 # (*) PyPy locks its GIL (see RPyGilAcquire) by manually doing atomic cmpxchg
 # and other games, which TSAN cannot see if PyPy itself was not compiled with
 # -fsanitize=thread.
-    {      py27,py36,py37d,py37           }-{thread       }-tsan
-# XXX see ^^^ about gevent vs python2-dbg
-    {py27d                                }-{thread       }-tsan
+    {py27d,py27,py36,py37d,py37           }-{thread       }-tsan
 # XXX py*-gevent-tsan would be nice to have, but at present TSAN is not
 # effective with gevent, because it does not understand greenlet "thread"
 # switching and so perceives the program as having only one thread where races
 # are impossible. Disabled to save time.
-#   {      py27,py36,py37d,py37           }-{       gevent}-tsan
+#   {py27d,py27,py36,py37d,py37           }-{       gevent}-tsan
 
 
 # AddressSanitizer