Update buildingWithSPM.md

swift build clean updated to swift package clean in 4.0

Author: Pinwheeler

guide/buildingWithSPM.md

@@ -108,11 +108,7 @@ swift build
 This command will download any dependencies if they haven't been already acquired and attempt to build the project. If the build is successful, then the resulting executable will be placed in the (hidden) ```.build/debug/``` directory. When building the PerfectTemplate project, you will see as the last line of SPM output: ```Linking .build/debug/PerfectTemplate```. Entering ```.build/debug/PerfectTemplate``` will run the server. By default, a debug version of the executable will be generated. To build a production ready release version, you would issue the command ```swift build -c release```. This will place the resulting executable in the ```.build/release/``` directory.
 
 ```
-swift build --clean
-```
-
-```
-swift build --clean=dist
+swift package clean
 ```
 
 It can be useful to wipe out all intermediate data and do a fresh build. Providing the ```--clean``` argument will delete the ```.build``` directory, and permit a fresh build. Providing the ```--clean=dist``` argument will delete both the ```.build``` directory and the ```Packages``` directory. Doing so will re-download all project dependencies during the next build to ensure you have the latest version of a dependent project.