readability: rs-rollback

Before
---
file: build/rs-rollbacks/json/core/replica-set-rollbacks.json
source: source/core/replica-set-rollbacks.txt
stats:
   coleman-liau: 12.018120481927706
   flesch-ease: 42.9857450856056
   flesch-level: 12.68986683576411
   foggy:
      count: 35
      factor: 0.08433734939759036
      threshold: 3
   sentence-count: 19
   sentence-len-avg: 21
   smog-index: 10.882677951670543
   word-count: 415

After
---
file: build/rs-rollbacks/json/core/replica-set-rollbacks.json
source: source/core/replica-set-rollbacks.txt
stats:
   coleman-liau: 11.282389610389611
   flesch-ease: 47.12029220779223
   flesch-level: 11.034480519480518
   foggy:
      count: 32
      factor: 0.08311688311688312
      threshold: 3
   sentence-count: 22
   sentence-len-avg: 17
   smog-index: 10.018931242160765
   word-count: 385

Signed-off-by: Sam Kleinman <samk@10gen.com>
minor: edits to rs-rollback