changed filament diameter for consistency between all example config files.

Marlin/example_configurations/Hephestos_2/Configuration.h

 // Uncomment below to enable
 //#define FILAMENT_WIDTH_SENSOR
 
-#define DEFAULT_NOMINAL_FILAMENT_DIA 1.75  //Enter the diameter (in mm) of the filament generally used (3.0 mm or 1.75 mm) - this is then used in the slicer software.  Used for sensor reading validation
+#define DEFAULT_NOMINAL_FILAMENT_DIA 3.00  //Enter the diameter (in mm) of the filament generally used (3.0 mm or 1.75 mm) - this is then used in the slicer software.  Used for sensor reading validation
 
 #if ENABLED(FILAMENT_WIDTH_SENSOR)
   #define FILAMENT_SENSOR_EXTRUDER_NUM 0   //The number of the extruder that has the filament sensor (0,1,2)

Marlin/example_configurations/delta/biv2.5/Configuration.h

 // Uncomment below to enable
 //#define FILAMENT_WIDTH_SENSOR
 
-#define DEFAULT_NOMINAL_FILAMENT_DIA 1.75  //Enter the diameter (in mm) of the filament generally used (3.0 mm or 1.75 mm) - this is then used in the slicer software.  Used for sensor reading validation
+#define DEFAULT_NOMINAL_FILAMENT_DIA 3.00  //Enter the diameter (in mm) of the filament generally used (3.0 mm or 1.75 mm) - this is then used in the slicer software.  Used for sensor reading validation
 
 #if ENABLED(FILAMENT_WIDTH_SENSOR)
   #define FILAMENT_SENSOR_EXTRUDER_NUM 0   //The number of the extruder that has the filament sensor (0,1,2)

Marlin/example_configurations/delta/kossel_xl/Configuration.h

 // Uncomment below to enable
 //#define FILAMENT_WIDTH_SENSOR
 
-#define DEFAULT_NOMINAL_FILAMENT_DIA 1.75  //Enter the diameter (in mm) of the filament generally used (3.0 mm or 1.75 mm) - this is then used in the slicer software.  Used for sensor reading validation
+#define DEFAULT_NOMINAL_FILAMENT_DIA 3.00  //Enter the diameter (in mm) of the filament generally used (3.0 mm or 1.75 mm) - this is then used in the slicer software.  Used for sensor reading validation
 
 #if ENABLED(FILAMENT_WIDTH_SENSOR)
   #define FILAMENT_SENSOR_EXTRUDER_NUM 0   //The number of the extruder that has the filament sensor (0,1,2)