fix typo

Author: OutOfScopeia

docs/v4-recipes/build/add-build-script.md

@@ -20,7 +20,7 @@ dotnet new console -lang f# -n Build -o .
 
 Open the project you just created in your IDE and rename the module it contains from `Program.fs` to `Build.fs`.
 
-This renaming is't explicitly necessary, however it keeps your solution consistent with other SAFE apps and is a better name for the file really.
+This renaming isn't explicitly necessary, however it keeps your solution consistent with other SAFE apps and is a better name for the file really.
 
 > If you just rename the file directly rather than in your IDE, then the Build project won't be able to find it unless you edit the Build.fsproj file as well