Fix case of k in exaplanation.

Author: fumikito

src/DB_Command.php

@@ -660,9 +660,9 @@ public function tables( $args, $assoc_args ) {
 	 *  - gb (gigabytes)
 	 *  - tb (terabytes)
 	 *  - B   (ISO Byte setting, with no conversion)
-	 *  - KB  (ISO Kilobyte setting, with 1 kB  = 1,000 B)
+	 *  - KB  (ISO Kilobyte setting, with 1 KB  = 1,000 B)
 	 *  - KiB (ISO Kibibyte setting, with 1 KiB = 1,024 B)
-	 *  - MB  (ISO Megabyte setting, with 1 MB  = 1,000 kB)
+	 *  - MB  (ISO Megabyte setting, with 1 MB  = 1,000 KB)
 	 *  - MiB (ISO Mebibyte setting, with 1 MiB = 1,024 KiB)
 	 *  - GB  (ISO Gigabyte setting, with 1 GB  = 1,000 MB)
 	 *  - GiB (ISO Gibibyte setting, with 1 GiB = 1,024 MiB)