Accept Buffer and Buffer[] in typings for key, cert, and ca

These options are passed directly to `tls.createSecureContext`,
which supports `Buffer` and `Buffer[]` as argument types.

This makes the 'Connecting over encrypted connection' example
compile with TypeScript (since it uses a Buffer from 'fs.readFileSync')

Author: Aaron1011

typings/mysql/lib/Connection.d.ts

@@ -188,24 +188,24 @@ declare namespace Connection {
         pfx?: string;
 
         /**
-         * A string holding the PEM encoded private key
+         * Either a string/buffer or list of strings/Buffers holding the PEM encoded private key(s) to use
          */
-        key?: string;
+        key?: string | string[] | Buffer | Buffer[];
 
         /**
          * A string of passphrase for the private key or pfx
          */
         passphrase?: string;
 
         /**
-         * A string holding the PEM encoded certificate
+         * A string/buffer or list of strings/Buffers holding the PEM encoded certificate(s)
          */
-        cert?: string;
+        cert?: string | string[] | Buffer | Buffer[];
 
         /**
-         * Either a string or list of strings of PEM encoded CA certificates to trust.
+         * Either a string/Buffer or list of strings/Buffers of PEM encoded CA certificates to trust.
          */
-        ca?: string | string[];
+        ca?: string | string[] | Buffer | Buffer[];
 
         /**
          * Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)