Upgrading for clean compilation with openjdk-10

[RockyRoad29]

When building using make, I had the following errors:

javac -source 1.5 -target 1.5 src/org/flatland/drip/Main.java src/org/flatland/drip/Switchable.java src/org/flatland/drip/SwitchableInputStream.java src/org/flatland/drip/SwitchableOutputStream.java -d classes/
warning: [options] bootstrap class path not set in conjunction with -source 5
error: Source option 5 is no longer supported. Use 6 or later.
error: Target option 1.5 is no longer supported. Use 1.6 or later.
make: *** [Makefile:13: classes/org/flatland/drip/Main.class] Error 2

If I replace them with 1.6, I got:

warning: [options] bootstrap class path not set in conjunction with -source 6
warning: [options] source value 6 is obsolete and will be removed in a future release
warning: [options] target value 1.6 is obsolete and will be removed in a future release
warning: [options] To suppress warnings about obsolete options, use -Xlint:-options.

But we don't need them anymore AFAIK. So I just dropped the options. Then another warning came up:

src/drip_daemon.c:46:5: warning: implicit declaration of function ‘wait’ [-Wimplicit-function-declaration]

So I fixed that one according to https://stackoverflow.com/questions/41884685/implicit-declaration-of-function-wait

Thank you devs !