Make is_text_col's search case-insensitive for sqlite support (#177)

When using wp-sqlite-db as the back end for WordPress, wpcli's `search-replace` command fails because wp-sqlite-db returns text column types as `TEXT`, and wpcli search-replace checks whether a column is textual in `is_text_col` with `strpos` for "text" or "varchar". If this were `stripos` instead of `strpos` then this problem would be resolved, which would be nice, and I don't believe there would be any backward compatibility implications. So, here's a one-character PR :-)

(Of course, sqlite as backend isn't actually supported, but this is a fairly small change which should make things better for that without affecting the mainline code. I've also proposed aaemnnosttv/wp-sqlite-db#56 to wp-sqlite-db to have that return lowercase "text" for column types as well, thus hopefully fixing the problem at both ends.)

Author: stuartlangridge

src/Search_Replace_Command.php

@@ -712,7 +712,7 @@ private static function get_columns( $table ) {
 
 	private static function is_text_col( $type ) {
 		foreach ( array( 'text', 'varchar' ) as $token ) {
-			if ( false !== strpos( $type, $token ) ) {
+			if ( false !== stripos( $type, $token ) ) {
 				return true;
 			}
 		}