Trivial: Fix typo in key.h comment

[bitstein]

As spotted by user Blinken: https://bitcointalk.org/index.php?topic=1828929.msg18205985#msg18205985

In the bitcoin core file key.h there is a typo:

//! Check whether the 32-byte array pointed to be vch is valid keydata.
     bool static Check(const unsigned char* vch);

The comment should read:

//! Check whether the 32-byte array pointed to by vch is valid keydata.

[paveljanik]

ACK f490dae

[practicalswift]

ACK f490dae

[fanquake]

trivial ACK f490dae