fix signedness
fix signedness

Signed-off-by: dmitriy kalinin <0638f5af938d97bf839390c6283ef9e40c331b8e@pivotallabs.com>

cppforlife/checkman,Pivotal-DataFabric/checkman,cppforlife/checkman,cppforlife/checkman,Amit-PivotalLabs/checkman,Amit-PivotalLabs/checkman,cppforlife/checkman,Pivotal-DataFabric/checkman,Amit-PivotalLabs/checkman,Pivotal-DataFabric/checkman,Amit-PivotalLabs/checkman,Pivotal-DataFabric/checkman,Pivotal-DataFabric/checkman,cppforlife/checkman,Amit-PivotalLabs/checkman,cppforlife/checkman,Amit-PivotalLabs/checkman,Pivotal-DataFabric/checkman