install wheel

otherwise install of jsonschema fails

Author: Vladimir Kotal

opengrok-tools/pom.xml

@@ -206,6 +206,7 @@ Portions Copyright (c) 2017-2018, Chris Fraire <[email protected]>.
                                 <argument>pip</argument>
                                 <argument>setuptools</argument>
                                 <argument>certifi</argument>
+                                <argument>wheel</argument>
                             </arguments>
                         </configuration>
                         <phase>test</phase>