12_ENCODE: fix mark names to match referenced papers

[bvoight]

1. In-class Q3 states that H3K4me3 is associated with enhancers but the reading said that H3K4me1 was the enhancer mark.

2. The HW Q1 has H3K9ac as a repressive mark but the reading discussed H3K9me3 as the repressive chromatin mark.

So we should either rephrase the specifics of the question with the correct information in the paper, and/or change the marks that are referred to. e.g., Q3, change from them using H3K4me3 to H3K4me1 instead. or H3K9me3 in HW Q1.