Make targets.host UNIQUE, which auto-creates index

Done in regards to: https://github.com/brave/browser-ios/issues/310
Creating the index massively boosts performance for equality queries

preload-httpse.js

@@ -53,7 +53,7 @@ var db = new sqlite3.Database('httpse.sqlite', function (err) {
   db.exec(['DROP TABLE IF EXISTS rulesets',
           'CREATE TABLE rulesets (id INTEGER PRIMARY KEY, contents TEXT)',
           'DROP TABLE IF EXISTS targets',
-          'CREATE TABLE targets (host TEXT, ids TEXT)'].join('; '), function (err) {
+          'CREATE TABLE targets (host TEXT UNIQUE, ids TEXT)'].join('; '), function (err) {
     if (err !== null) {
       throw new Error('FATAL: could not create tables: ' + err)
     }