BME280: Increase sensor timeout (esphome#727)

I'm facing some occasional timeouts when reading BME280. 
Looking at Adafruit driver (that this code is based on), I see that base math is using 1.25ms, increased by 2.3*oversampliing + 0.575 for each value being read. 
I've added 1.5ms as baseline, to be on the same safe.

esphome/components/bme280/bme280.cpp

@@ -178,7 +178,7 @@ void BME280Component::update() {
     return;
   }
 
-  float meas_time = 1;
+  float meas_time = 1.5;
   meas_time += 2.3f * oversampling_to_time(this->temperature_oversampling_);
   meas_time += 2.3f * oversampling_to_time(this->pressure_oversampling_) + 0.575f;
   meas_time += 2.3f * oversampling_to_time(this->humidity_oversampling_) + 0.575f;