Fix camelcase consistency for mempool calls

[johnbailon]

Small fix on camelCase consistency for mempool call.

[ruimarinho]

I see that Travis tests are failing but it's unrelated to your PR (should have used a fixed Docker image). How angry does this inconsistency makes you feel :-)? This would require a major version due to the breaking change..

[johnbailon]

@ruimarinho haha, don't sweat it. I ran into it and thought it should make for a nice pull request. Feel free to wait for other fixes to make the major version bump worth it.

[ruimarinho]

This will likely be merged when the returned numbers are changed to be returned as strings.

[ruimarinho]

@johnbailon I'm more inclined to rename the other methods to Mempool instead of MemPool.

[johnbailon]

@ruimarinho why so? Do note that bitcoind's docs use MemPool.

[ruimarinho]

@johnbailon most people are using mempool or Mempool:

• Mempool package tracking bitcoin/bitcoin#6654
• [Mempool] Improve removal of invalid transactions after reorgs bitcoin/bitcoin#6915
• https://blockchain.info/charts/mempool-size
• https://themerkle.com/what-is-the-bitcoin-mempool/

Looks like the only place where MemPool is used is in the bitcoin developer reference docs.

[promag]

The fix should be s/MemPool/Mempool.