important fix -- apache shoots at air units again

Apache Helicopter wasn't shooting at air units. Now it does again.
bike rocket damage slightly tweaked++

Bike rocket damage increased to 30.
This lets it kill MLRS in 4 shots instead of 5. Important for the role the bike plays.
Kills Buggy in 4 shots instead of 5 as well. 
This helps to justify bike's cost of $500. Its primary job is to exploit open space with its speed to attack vulnerable units, e.g. go behind enemy lines and quickly kill artillery. 5 shots (3 volleys instead of 2) makes this far weaker in this role, and expensive to take the risk with.
fixed earlier mistake w/ mlrs HP

I made a mistake changing MLRS HP from 120 -> 115 in last patch. (I misread a unit stat and so the change didn't do the thing I thought, and had no purpose).

Returned to previous value of 120.
Merge pull request #2909 from psydev/patch-4

important fix -- apache shoots at air units again