edits and readbility fixes to arbiters page:

Stats:

Before
---
file: build/master/json/core/replica-set-arbiter.json
source: source/build/master/json/core/replica-set-arbiter.txt
stats:
   coleman-liau: 10.170030581039754
   flesch-ease: 43.763087989991675
   flesch-level: 10.847796775090355
   foggy:
      count: 19
      factor: 0.0581039755351682
      threshold: 3
   sentence-count: 22
   sentence-len-avg: 14
   smog-index: 8.438071523408619
   word-count: 327

After
---
file: build/master/json/core/replica-set-arbiter.json
source: source/build/master/json/core/replica-set-arbiter.txt
stats:
   coleman-liau: 10.725673758865245
   flesch-ease: 44.78580000000002
   flesch-level: 9.81487375886525
   foggy:
      count: 18
      factor: 0.06382978723404255
      threshold: 3
   sentence-count: 25
   sentence-len-avg: 11
   smog-index: 7.976525956113203
   word-count: 282
edits+readability for replica-set-members:

Before:
---
file: build/master/json/core/replica-set-members.json
source: source/build/master/json/core/replica-set-members.txt
stats:
   coleman-liau: 11.510803324099722
   flesch-ease: 37.63714650661743
   flesch-level: 11.99558818097876
   foggy:
      count: 64
      factor: 0.0886426592797784
      threshold: 3
   sentence-count: 45
   sentence-len-avg: 16
   smog-index: 9.941947471260946
   word-count: 722

After:
---
file: build/master/json/core/replica-set-members.json
source: source/build/master/json/core/replica-set-members.txt
stats:
   coleman-liau: 11.326474622770917
   flesch-ease: 38.80385858585862
   flesch-level: 11.13976655443322
   foggy:
      count: 66
      factor: 0.09053497942386832
      threshold: 3
   sentence-count: 55
   sentence-len-avg: 13
   smog-index: 9.3871
   word-count: 729
DOCS-1641: fixing pdf urls