Merge pull request #8 from markasoftware/markasoftware/math-and-wificlient

correct math.h header and specify wificlient as per new http library requirement.

examples/C02_PM_SHT_OLED_WIFI/C02_PM_SHT_OLED_WIFI.ino

@@ -39,6 +39,8 @@ AirGradient ag = AirGradient();
 
 SSD1306Wire display(0x3c, SDA, SCL);
 
+WiFiClient client;
+
 // set sensors that you do not use to false
 boolean hasPM=true;
 boolean hasCO2=true;