Make Numulus compile on macOS (#1070)

* Make Numulus compile on macOS

BSD sed behaves differently than Linux sed. By adding a "-e" flag the
comand works in both systems.

See: https://unix.stackexchange.com/questions/101059/sed-behaves-different-on-freebsd-and-on-linux

* Make the regex easier to understand

core/build.gradle

@@ -423,7 +423,7 @@ task jaxbToJava {
       }
     }
     execInBash(
-        'find . -name *.java -exec sed -i /\\*\\ \\<p\\>\\$/d {} +',
+        "find . -name *.java -exec sed -i -e '/" + /\* <p>$/ + "/d' {} +",
         generatedDir)
   }
 }