Fix base mutations

[RK900]

Problems

1. Base mutations are only to 4 (C)
2. Previous mutated sequence carries over to next iteration

Example:

Should be:

# this is for only 1 randomly generated sequence
[4 2 4 4 2 2 3 1 2]
[1 2 4 4 2 2 3 1 2]  [2 2 4 4 2 2 3 1 2]  [3 2 4 4 2 2 3 1 2]  [4 2 4 4 2 2 3 1 2]
# calculate reward
[4 2 4 4 2 2 3 1 2]
[4 1 4 4 2 2 3 1 2]  [4 2 4 4 2 2 3 1 2]  [4 3 4 4 2 2 3 1 2]  [4 4 4 4 2 2 3 1 2]
# calculate reward

Currently is:

[4 2 4 4 2 2 3 1 2]
[4 2 4 4 2 2 3 1 2]  [4 2 4 4 2 2 3 1 2]  [4 2 4 4 2 2 3 1 2]  [4 2 4 4 2 2 3 1 2]
# calculate reward
[4 2 4 4 2 2 3 1 2]
[4 4 4 4 2 2 3 1 2]  [4 4 4 4 2 2 3 1 2]  [4 4 4 4 2 2 3 1 2]  [4 4 4 4 2 2 3 1 2]
# calculate reward

Eventually, the entire list becomes 4s.