Trivial: Fix typo in key.h comment

Author: bitstein

src/key.h

@@ -45,7 +45,7 @@ class CKey
     //! The actual byte data
     std::vector<unsigned char, secure_allocator<unsigned char> > keydata;
 
-    //! Check whether the 32-byte array pointed to be vch is valid keydata.
+    //! Check whether the 32-byte array pointed to by vch is valid keydata.
     bool static Check(const unsigned char* vch);
 
 public: