handle json reading exception instead of escalating

V, 2016-11-16 16:00:00, 7818/7819 S (100.0%), 7815/7815 E (100.0%)
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2016-11-16 16:06:15,696 ERROR o.t.c.c.CollecTorMain:71 The relaydescs
module failed: com.google.gson.stream.MalformedJsonException: Use
JsonReader.setLenient(true) to accept malformed JSON at line 1 column
17791699
com.google.gson.JsonSyntaxException:
com.google.gson.stream.MalformedJsonException: Use
JsonReader.setLenient(true) to accept malformed JSON at line 1 column
17791699
    at com.google.gson.Gson.assertFullConsumption(Gson.java:779)
~[collector-1.1.0.jar:1.1.0-d9e32d5]
    at com.google.gson.Gson.fromJson(Gson.java:742)
~[collector-1.1.0.jar:1.1.0-d9e32d5]
    at org.torproject.collector.relaydescs.ReferenceChecker.readReferencesFile(ReferenceChecker.java:145)
~[collector-1.1.0.jar:1.1.0-d9e32d5]
    at org.torproject.collector.relaydescs.ReferenceChecker.check(ReferenceChecker.java:84)
~[collector-1.1.0.jar:1.1.0-d9e32d5]