fix method reference of set of incorrect type

[richardstephens]

filterConflictsBy expects a predicate that operates on a Conflict, but the code passes a method reference to categoriesToInclude::contains, which is a set of type ConflictCategory. Instead, pass a lambda to check if the conflict's category is in the set.

Discovered while porting the Maven implemenation to run with Bazel

[codecov[bot]]

Codecov Report

Merging #302 (19a4eb6) into master (10a26fe) will decrease coverage by 4.48%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #302      +/-   ##
============================================
- Coverage     85.20%   80.73%   -4.48%     
+ Complexity      237      232       -5     
============================================
  Files            23       23              
  Lines           872      872              
  Branches        104      104              
============================================
- Hits            743      704      -39     
- Misses           92      129      +37     
- Partials         37       39       +2     

Impacted Files	Coverage Δ
.../java/com/spotify/missinglink/maven/CheckMojo.java	89.28% <100.00%> (-0.80%)	:arrow_down:
...ava/com/spotify/missinglink/Java9ModuleLoader.java	0.00% <0.00%> (-78.58%)	:arrow_down:
...otify/missinglink/datamodel/MethodDescriptors.java	79.31% <0.00%> (-6.90%)	:arrow_down:
...n/java/com/spotify/missinglink/ArtifactLoader.java	79.72% <0.00%> (-1.36%)	:arrow_down:
.../java/com/spotify/missinglink/ConflictChecker.java	86.53% <0.00%> (-0.65%)	:arrow_down:

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[mattnworb]

https://github.com/spotify/missinglink/releases/tag/v0.2.7