fix(store): TTL should range 1..n rather than 1..n+1

was experiencing intermittent functional test fails where TTL was eg 101 when 100 was expected
informal testing on a windows platform shows Go times resolving to the nanosecond but with an accuracy of approximately 1 millisecond
I believe some of the functional test steps would run in under a millisecond and cause the TTL to be recomputed with the same time.Now() value resulting in a TTL that was +1 from the expected
for context, here is some accuracy discussion: http://stackoverflow.com/a/14611355