Extract Convert.ChangeType into a new ConvertString method

The purpose of this commit is to trigger CI on AppVeyor to verify that all tests are passing since 30 of them do not pass on my machine (macOS 10.12.6 with JetBrains Rider 2017.3 and mono 5.4.1.7)

Author: 0xced

src/CommandLine/Core/TypeConverter.cs

@@ -49,6 +49,11 @@ private static Maybe<object> ChangeTypeScalar(string value, Type conversionType,
             return result.ToMaybe();
         }
 
+        private static object ConvertString(string value, Type type, CultureInfo conversionCulture)
+        {
+            return Convert.ChangeType(value, type, conversionCulture);
+        }
+        
         private static Result<object, Exception> ChangeTypeScalarImpl(string value, Type conversionType, CultureInfo conversionCulture, bool ignoreValueCase)
         {
             Func<object> changeType = () =>
@@ -71,10 +76,9 @@ private static Result<object, Exception> ChangeTypeScalarImpl(string value, Type
                         () =>
 #if !SKIP_FSHARP
                             isFsOption
-                                ? FSharpOptionHelper.Some(type, Convert.ChangeType(value, type, conversionCulture)) :
+                                ? FSharpOptionHelper.Some(type, ConvertString(value, type, conversionCulture)) :
 #endif
-                                Convert.ChangeType(value, type, conversionCulture);
-
+                                ConvertString(value, type, conversionCulture);
 #if !SKIP_FSHARP
                     Func<object> empty = () => isFsOption ? FSharpOptionHelper.None(type) : null;
 #else