SCB-260 Clarify copyright of HystrixCommandPropertiesExt

[yangbor]

The majority of the HystrixCommandPropertiesExt class is forked
from the base class. Thus we need to keep the original copyright.

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[coveralls]

Coverage increased (+0.02%) to 87.261% when pulling 7e0bda2 on yangbor:master into cfc66b9 on apache:master.