Revert to PyPy 7.3.1.

docs/changes/issue1692.misc

-Travis CI now tests PyPy 7.3.2.
+PyPy 7.3.2 (2.7 and 3.6) have been tested, and a small issue with 2.7
+was corrected.
+
+These are not yet tested on Travis CI.
 
 .. note:: Support for Python 3.5 will be removed in 2021, as it has
           now reached end-of-life.

scripts/install.sh

@@ -120,13 +120,13 @@ for var in "$@"; do
             install 3.8.2 python3.8 3.8.d
             ;;
         3.9)
-            install 3.9-dev python3.9 3.9.d
+            install 3.9.0 python3.9 3.9.d
             ;;
         pypy2.7)
-            install pypy2.7-7.3.2 pypy2.7 pypy2.7.d
+            install pypy2.7-7.3.1 pypy2.7 pypy2.7.d
             ;;
         pypy3.6)
-            install pypy3.6-7.3.2 pypy3.6 pypy3.6.d
+            install pypy3.6-7.3.1 pypy3.6 pypy3.6.d
             ;;
     esac
 done