Cisco IOS Fix missing extraction case for pfs group20

[arifogel]

• fixes Diffie-Hellman Group 20 is missing in config parser for Cisco IOS #7987

[batfish-bot]

This change is 

[ratulm]

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @corinaminer and @dhalperi)

[codecov]

Codecov Report

Merging #7994 (a21e090) into master (4ba453e) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #7994      +/-   ##
============================================
- Coverage     74.29%   74.28%   -0.01%     
+ Complexity    42831    42827       -4     
============================================
  Files          3346     3346              
  Lines        168027   168029       +2     
  Branches      20134    20135       +1     
============================================
- Hits         124834   124827       -7     
- Misses        33600    33603       +3     
- Partials       9593     9599       +6     

Impacted Files	Coverage Δ
...fish/grammar/cisco/CiscoControlPlaneExtractor.java	62.11% <100.00%> (+0.22%)	⬆️
...src/main/java/org/batfish/coordinator/PoolMgr.java	54.76% <0.00%> (-5.96%)	⬇️
...fish/bddreachability/BDDLoopDetectionAnalysis.java	80.23% <0.00%> (-2.33%)	⬇️
...model/routing_policy/communities/CommunitySet.java	93.84% <0.00%> (-1.54%)	⬇️
...main/java/org/batfish/datamodel/acl/AclTracer.java	63.69% <0.00%> (-1.28%)	⬇️
...ain/java/org/batfish/datamodel/EvpnType3Route.java	70.70% <0.00%> (-1.02%)	⬇️
...ain/java/org/batfish/coordinator/WorkQueueMgr.java	70.93% <0.00%> (-0.59%)	⬇️
...src/main/java/org/batfish/coordinator/WorkMgr.java	75.38% <0.00%> (-0.47%)	⬇️
...java/org/batfish/dataplane/ibdp/VirtualRouter.java	87.46% <0.00%> (-0.26%)	⬇️