Fix 2 flaky tests in class FluentIterableTest.

[LALAYANG]

1. Test failures:
   • Run: mvn -pl guava edu.illinois:nondex-maven-plugin:1.1.2:nondex -Dtest=com.fasterxml.jackson.datatype.guava.FluentIterableTest, *Here are the details of NonDex.
   • Two tests fail: com.fasterxml.jackson.datatype.guava.FluentIterableTest.testSerialization com.fasterxml.jackson.datatype.guava.FluentIterableTest.testWrappedSerialization

• The failures:

  at com.fasterxml.jackson.datatype.guava.FluentIterableTest.testSerialization(FluentIterableTest.java:37)
  [ERROR] Failures:
  [ERROR]   FluentIterableTest.testSerialization:37 expected:<[[1,2,3]]> but was:<[[3,1,2]]>

  at com.fasterxml.jackson.datatype.guava.FluentIterableTest.testWrappedSerialization(FluentIterableTest.java:43)
  [ERROR] Failures:
  [ERROR]   FluentIterableTest.testWrappedSerialization:43 expected:<{"value":[[1,2,3]]}> but was:<{"value":[[3,1,2]]}>

  2. Why they fail:
• The 2 tests fail for the same reason, MAPPER.writeValueAsString() serializes Java objects as JSON output, but the order of objects being mapped into a string by ObjectMapper changes, resulting in a different serialized JSON string.
  3. Fix them:
• Check JSON results by JSONAssert and test assertions changes, also need to add the dependency for org.skyscreamer.jsonassert.

[cowtowncoder]

First of all, thank you for contributing this! Fix would be great.

Just onet thing: I do not want to add a new dependency for just one test. It'd be great to do the test using just Jackson (or simple String processing.

[cowtowncoder]

Oh actually I see: it is iterating over the hash set contents.

[cowtowncoder]

@LALAYANG I figured that an even simpler way is to ensure iteration order is set, which happens when using a List.

Thank you once again for identifying the issue!