fix doctests

[pgrepds]

I have fixed all jldoctest as proposed by issue #192.

There are some cases for which I have deactivated the jldoctest and which might need further attention.

I have deactivated the following jldoctests

• modularity.jl has a reference on SimpleWeightedGraph which is not included by Graphs.jl.
• transitivity.jl in the function transitiveClosure. The issue here is that Documenter.jl truncates the output. Thus, it is not fully visible. We could compare the truncated output instead. However, it might then differ from the output which is seen by the user.
• shortestpaths.jl in the function has_negative_weight_cycle in src/Experimental. The SPFA package is not found. The same happens in spfa.jl.
• spfa.jl in spfa_shortest_paths. The output is compared to an error message. However, the full stack trace is obviously not included.
• euclidiagraphs.jl uses random values. We might want to add a local doc filter.
• randgraphs.jl uses random values. We might want to add a local doc filter here as well.

[gdalle]

Thanks for the painstaking work @pgrepds, this will definitely increase code reliability!!!

[codecov]

Codecov Report

Merging #239 (7213fc5) into master (5649092) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #239   +/-   ##
=======================================
  Coverage   97.23%   97.23%           
=======================================
  Files         114      114           
  Lines        6583     6583           
=======================================
  Hits         6401     6401           
  Misses        182      182