Use SET syntax as specified in the MySQL documentation (#1402)

Author: beautifulentropy

Diff for: AUTHORS

@@ -83,6 +83,7 @@ Reed Allman <rdallman10 at gmail.com>
 Richard Wilkes <wilkes at me.com>
 Robert Russell <robert at rrbrussell.com>
 Runrioter Wung <runrioter at gmail.com>
+Samantha Frank <hello at entropy.cat>
 Santhosh Kumar Tekuri <santhosh.tekuri at gmail.com>
 Sho Iizuka <sho.i518 at gmail.com>
 Sho Ikeda <suicaicoca at gmail.com>

Diff for: connection.go

@@ -71,10 +71,10 @@ func (mc *mysqlConn) handleParams() (err error) {
 				cmdSet.Grow(4 + len(param) + 1 + len(val) + 30*(len(mc.cfg.Params)-1))
 				cmdSet.WriteString("SET ")
 			} else {
-				cmdSet.WriteByte(',')
+				cmdSet.WriteString(", ")
 			}
 			cmdSet.WriteString(param)
-			cmdSet.WriteByte('=')
+			cmdSet.WriteString(" = ")
 			cmdSet.WriteString(val)
 		}
 	}