fix off-by-one error in update check for db-version/56

We missed an off-by-one in my previous DB change:
90467bf8bf2f8e4a46cb1db563154df4035bf746

This causes the installed app parsing to happen on each start when on any
build that is on db-version/56.  Its not a big deal since the broken code
was not shipped at all, even in an alpha.

app/src/main/java/org/fdroid/fdroid/data/DBHelper.java

@@ -566,7 +566,7 @@ class DBHelper extends SQLiteOpenHelper {
      * table for the first time.
      */
     private void recreateInstalledAppTable(SQLiteDatabase db, int oldVersion) {
-        if (oldVersion >= 57) {
+        if (oldVersion >= 56) {
             return;
         }
         Utils.debugLog(TAG, "(re)creating 'installed app' database table.");