limit Redis keys length

[malafeev]

fix for #17

[coveralls]

Pull Request Test Coverage Report for Build 84

• 54 of 133 (40.6%) changed or added relevant lines in 9 files are covered.
• 4 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.2%) to 4.523%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
opentracing-redis-lettuce/src/main/java/io/opentracing/contrib/redis/lettuce/TracingRedisAsyncCommands.java	4	5	80.0%
opentracing-redis-lettuce/src/main/java/io/opentracing/contrib/redis/lettuce/TracingRedisCommands.java	3	4	75.0%
opentracing-redis-common/src/main/java/io/opentracing/contrib/redis/common/TracingHelper.java	7	10	70.0%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisSentinelPool.java	4	14	28.57%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedis.java	1	18	5.56%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisCluster.java	0	17	0.0%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisPool.java	4	34	11.76%

Files with Coverage Reduction	New Missed Lines	%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedis.java	2	0.28%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisCluster.java	2	0.0%

Totals
Change from base Build 80:	0.2%
Covered Lines:	485
Relevant Lines:	10723

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💛 - Coveralls