Broken heat.exe in package WiX with version=3.11.1

### What You Are Seeing?
Broken heat.exe in package WiX with version=3.11.1

**heat.exe : error HEAT0001 : An error occurred loading a configuration file: The parameter 'exePath' is invalid.**

### What is Expected?
Creation of wxs file
### What version of Cake are you using?
0.32.1
### Are you running on a 32 or 64 bit system?
64
### What environment are you running on? Windows? Linux? Mac?
Windows
### Are you running on a CI Server? If so, which one?
No

### How Did You Get This To Happen? (Steps to Reproduce)
Tested in two projects one netcoreapp2.2, another netcoreapp2.1 (https://github.com/wieslawsoltes/Core2D)
In "Core2D\src\Core2D.UI.Avalonia"
- ` dotnet publish -c Release -f netcoreapp2.1`
- make build.cake and build.ps1 files
- paste to build.cake
```
#tool nuget:?package=WiX&version=3.11.1
var fileWXS = File("./Core2d.wxs");
DirectoryPath path = (DirectoryPath)Directory("./bin/AnyCPU/Release/netcoreapp2.1/publish");
WiXHeat(path, fileWXS, WiXHarvestType.Dir);
```
- ./build

### Output Log
~~~sh
Preparing to run build script...
Running build script...
heat.exe : error HEAT0001 : An error occurred loading a configuration file: The parameter 'exePath' is invalid.
Parameter name: exePath

Exception Type: System.Configuration.ConfigurationErrorsException

Stack Trace:
at System.Configuration.ConfigurationSchemaErrors.ThrowIfErrors(Boolean ignoreLocal)
at System.Configuration.BaseConfigurationRecord.ThrowIfParseErrors(ConfigurationSchemaErrors schemaErrors)
at System.Configuration.Configuration..ctor(String locationSubPath, Type typeConfigHost, Object[] hostInitConfigurationParams)
at System.Configuration.ClientConfigurationHost.OpenExeConfiguration(ConfigurationFileMap fileMap, Boolean isMachine, ConfigurationUserLevel userLevel, String exePath)
at System.Configuration.ConfigurationManager.OpenExeConfigurationImpl(ConfigurationFileMap fileMap, Boolean isMachine, ConfigurationUserLevel userLevel, String exePath, Boolean preLoad)
at Microsoft.Tools.WindowsInstallerXml.AppCommon.ReadConfiguration(StringCollection extensions)
at Microsoft.Tools.WindowsInstallerXml.Tools.Heat.Run(String[] args)
~~~

Start by reproducing the failure from the referenced Core2D project using the build.cake and build.ps1 steps, then inspect the WiXHeat call with WiX 3.11.1. Compare the generated command and configuration handling around the heat.exe invocation. Done means the command completes without HEAT0001 and creates the expected Core2d.wxs file.

Written by the indexing model from the issue text.