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

examples/config.py

@@ -21,7 +21,7 @@
 # }
 
 # java_paths = {
-#     '1.8': "/usr/lib/jvm/java-8-openjdk",
+#     '8': "/usr/lib/jvm/java-8-openjdk",
 # }
 
 # Build tools version to be used