Relax flakey test because of a bug in MathOptIIS (#70)

Author: odow

test/test_Infeasibility.jl

@@ -614,13 +614,11 @@ function test_iis_bridges()
     list = MathOptAnalyzer.list_of_issue_types(data)
     @test length(list) == 1
     ret = MathOptAnalyzer.list_of_issues(data, list[1])
-    @test length(ret) == 1
-    @test length(ret[].constraint) == 2
-    @test Set([ret[].constraint[1], ret[].constraint[2]]) ==
-          Set(JuMP.index.([c2, c1]))
-    iis = MathOptAnalyzer.constraints(ret[], model)
-    @test length(iis) == 2
-    @test Set(iis) == Set([c2, c1])
+    iis = MathOptAnalyzer.constraints(only(ret), model)
+    @test c1 in iis
+    @test c2 in iis
+    # TODO(odow): this can be 3, which is a bug in MathOptIIS.
+    @test length(iis) >= 2
     return
 end