Merge pull request #621 from HatiEth/patch-1

Update submodules.asc

Author: ben

book/07-git-tools/sections/submodules.asc

@@ -821,7 +821,7 @@ If you do remove it and then switch back to the branch that has that submodule,
 
 [source,console]
 ----
-$ git clean -fdx
+$ git clean -ffdx
 Removing CryptoLibrary/
 
 $ git checkout add-crypto