Fix formulas for InverseDegreeFahrenheit (#808)

Author: tmilnthorp

Common/UnitDefinitions/CoefficientOfThermalExpansion.json

@@ -42,8 +42,8 @@
       "BaseUnits": {
         "Θ": "DegreeFahrenheit"
       },
-      "FromUnitToBaseFunc": "x*5/9",
-      "FromBaseToUnitFunc": "x*9/5",
+      "FromUnitToBaseFunc": "x*9/5",
+      "FromBaseToUnitFunc": "x*5/9",
       "Localization": [
         {
           "Culture": "en-US",

UnitsNet.Tests/CustomCode/CoefficientOfThermalExpansionTests.cs

@@ -30,7 +30,7 @@ public class CoefficientOfThermalExpansionTests : CoefficientOfThermalExpansionT
     {
         protected override double InverseDegreeCelsiusInOneInverseKelvin => 1.0;
 
-        protected override double InverseDegreeFahrenheitInOneInverseKelvin => 1.8;
+        protected override double InverseDegreeFahrenheitInOneInverseKelvin => 0.5555555555555556;
 
         protected override double InverseKelvinInOneInverseKelvin => 1.0;
     }