Fix misleading java_path example

Fix misleading java_path example

As you can see in fdroidserver/common.py:219
for java_version in ('7', '8', '9'):
the code look for java version without the 1. in front, after getting a
bunch of error message that JDK could't be found, investigating the code
and documentation I discovered my configuration was ignored because of
this and realized the example was wrong