RSI, oversold start optimization (#1691)

* Update strategy.js

Correct code proposed in the second pull request.
This code is tested and works, actually I'm using whit this modifications and all works ok.
Sorry again for my error.

* Optimized RSI

Adding validation before execute all the conditionals

* Optimization RSI

Adding validation before execute all the conditionals

* Optimization RSI strategy

* Optimization RSI strategy

extensions/strategies/rsi/strategy.js

@@ -26,7 +26,7 @@ module.exports = {
   onPeriod: function (s, cb) {
     if (s.in_preroll) return cb()
     if (typeof s.period.rsi === 'number') {
-      if (s.trend !== 'oversold' && s.trend !== 'long' && s.period.rsi <= s.options.oversold_rsi) {
+      if (s.trend === undefined && s.period.rsi <= s.options.oversold_rsi) {
         s.rsi_low = s.period.rsi
         s.trend = 'oversold'
       }