fix: overflow in qgrams for k=32

[RagnarGrootKoerkamp]

For k exactly equal to 32 (or generally when the assertion above has exact
equality), the 1<<(q*bits) overflows, which is undefined in rust. This PR
makes it defined behaviour.

[coveralls]

Coverage increased (+0.09%) to 88.779% when pulling d31f971 on RagnarGrootKoerkamp:fix_shl_overflow into b244a21 on rust-bio:master.

[natir]

Hello,

Nice find, I think it could be a good idea to add a small test to be sure this bug didn't come back in future.

[RagnarGrootKoerkamp]

Good idea. done

[johanneskoester]

We need to raise the MSRV to 1.53 for this. @RagnarGrootKoerkamp may I ask you to update the readme and also the MSRV job here?

[RagnarGrootKoerkamp]

I could also use sizeof so the version doesn't need to be bumped. Or do you prefer to bump it anyway?

[RagnarGrootKoerkamp]

Updated MSRV to 1.53