docs: spelling fixes [ci skip]

Closes https://github.com/libssh2/libssh2/pull/222

docs/HACKING.CRYPTO

@@ -360,7 +360,7 @@ the public key is returned in `public'.
 
 int libssh2_dh_secret(_libssh2_dh_ctx *dhctx, _libssh2_bn *secret,
                       _libssh2_bn *f, _libssh2_bn *p, _libssh2_bn_ctx * bnctx)
-Computes the Diffie-Hellman secret from the previouly created context `*dhctx',
+Computes the Diffie-Hellman secret from the previously created context `*dhctx',
 the public key `f' from the other party and the same prime `p' used at
 context creation. The result is stored in `secret'.
 0 is returned upon success, else -1.

docs/SECURITY.md

@@ -96,5 +96,5 @@ libssh2 project and you have shown an understanding for the project and its way
 of working. You must've been around for a good while and you should have no
 plans in vanishing in the near future.
 
-We do not make the list of partipants public mostly because it tends to vary
+We do not make the list of participants public mostly because it tends to vary
 somewhat over time and a list somewhere will only risk getting outdated.