Fix wheel builds

Should fix #113.

We can't see if the fix works because wheels are built only for git
tags.

.manylinux-install.sh

@@ -9,7 +9,9 @@ for PYBIN in /opt/python/*/bin; do
        [[ "${PYBIN}" == *"cp36"* ]] || \
        [[ "${PYBIN}" == *"cp37"* ]] || \
        [[ "${PYBIN}" == *"cp38"* ]]; then
-        "${PYBIN}/pip" install -U pip setuptools wheel cffi
+        # NB: it's risky to upgrade wheel without upgrading auditwheel,
+        # see https://github.com/pypa/auditwheel/issues/206
+        "${PYBIN}/pip" install -U pip setuptools wheel cffi auditwheel
         "${PYBIN}/pip" install -e /io/
         "${PYBIN}/pip" wheel /io/ -w wheelhouse/
         rm -rf /io/build /io/*.egg-info