Add 3.8 to wheel builders. [skip ci]

scripts/releases/geventreleases.sh

@@ -18,6 +18,7 @@ mkdir /tmp/gevent/
 
 # 3.7 is a python.org build, builds a 10_6_intel wheel
 ./geventrel.sh /usr/local/bin/python3.7
+./geventrel.sh /usr/local/bin/python3.8
 
 
 # PyPy 4.0

scripts/releases/make-manylinux

@@ -12,7 +12,7 @@ if [ -d /gevent -a -d /opt/python ]; then
     cd /gevent
     rm -rf wheelhouse
     mkdir wheelhouse
-    for variant in `ls -d /opt/python/cp{27,35,36,37}*`; do
+    for variant in `ls -d /opt/python/cp{27,35,36,37,38}*`; do
         echo "Building $variant"
         mkdir /tmp/build
         cd /tmp/build