ramped up wind.world: increase windRampStart to 90s (#1044)

To give simulated vehicles more time to establish in air
before the wind is ramped up.

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

worlds/ramped_up_wind.world

@@ -20,7 +20,7 @@
       <windVelocityVariance>0</windVelocityVariance>
       <windDirectionMean>0 1 0</windDirectionMean>
       <windDirectionVariance>0</windDirectionVariance>
-      <windRampStart>60</windRampStart>
+      <windRampStart>90</windRampStart>
       <windRampWindVectorComponents>0 15 0</windRampWindVectorComponents>
       <windChangeRampDuration>30</windChangeRampDuration>
       <windGustStart>0</windGustStart>