Fix the Difficulty to what we imagined :D

Here's our fix to the difficulty of the game, as it turned out a lot more challenging than the balancer thought it was. 
(That's the result of balancing done by the main tester xD) 

The Update is mainly tweaks to buff friends and nerf enemies a bit and a lower the growth of difficulty in the waves.

Oh and we fixed a typo in the tutorial :D

Detailed Code Changes can be found in the GitHub Commit:
https://github.com/benitsch/Ludum-Dare-55/commit/53230c2ae2ce4ea59d19d359c0c9a6f...

The first version can still be found as the downloads meaning:

• Version - 07: is the first published entry for LD55
• Version - 08: has the difficulty fixed to better match what we imagined.