fix ProxyPass directive by adding mandatory trailing slash

examples/reverse-proxies/apache/matrix-domain.conf

@@ -29,7 +29,7 @@
 	RequestHeader set "X-Forwarded-Proto" expr=%{REQUEST_SCHEME}
 
 	AllowEncodedSlashes NoDecode
-	ProxyPass / http://127.0.0.1:81 retry=0 nocanon
+	ProxyPass / http://127.0.0.1:81/ retry=0 nocanon
 	ProxyPassReverse / http://127.0.0.1:81/
 
 	ErrorLog ${APACHE_LOG_DIR}/matrix.DOMAIN-error.log