Added key index

frontend/src/forecastCollection.js

@@ -28,8 +28,8 @@ const ForecastCollection = (props) => {
   if (forecast && forecast.city) {
     return (
       <div className="forecast-days">
-        {forecast.list.map(day => (
-          <div  className="forecasted-day">
+        {forecast.list.map((day, index) => (
+          <div key={index} className="forecasted-day">
             <p>{new Date(day.dt * 1000).toLocaleDateString('en-US', { weekday: 'long' })}</p>
             <img src={`${process.env.PUBLIC_URL}/weatherIconsFill/${day.weather[0].icon}.svg`} alt="weather icon" />
             <p>{day.weather[0].main}</p>