rem_vertex! bugfix

[jarbus]

Resolves an issue where properties that point from the last node to the last node don't get updated with the new vertex number, referenced in #87

The current version of MetaGraphs.jl fails with the following example:

using LightGraphs, MetaGraphs
g = MetaDiGraph(2)
add_edge!(g, 2, 2)
rem_vertex!(g, 1)

Yields

ERROR: LoadError: KeyError: key 1 not found
Stacktrace:
 [1] getindex
   @ ./dict.jl:482 [inlined]
 [2] rem_vertex!(g::MetaDiGraph{Int64, Float64}, v::Int64)
   @ MetaGraphs ~/.julia/packages/MetaGraphs/UlMik/src/MetaGraphs.jl:184

[codecov]

Codecov Report

Merging #125 (4af220c) into master (3a8b98c) will decrease coverage by 1.04%.
The diff coverage is 33.33%.

❗ Current head 4af220c differs from pull request most recent head eda4421. Consider uploading reports for the commit eda4421 to get more accurate results

@@            Coverage Diff             @@
##           master     #125      +/-   ##
==========================================
- Coverage   98.64%   97.60%   -1.05%     
==========================================
  Files           5        5              
  Lines         370      376       +6     
==========================================
+ Hits          365      367       +2     
- Misses          5        9       +4     

Impacted Files	Coverage Δ
src/MetaGraphs.jl	97.84% <33.33%> (-1.72%)	⬇️

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