Update projects.md

Fix typo: "if" -> "of"

Author: Prakash-Kuikel

docs/extensibility/vsix/tips/projects.md

@@ -14,7 +14,7 @@ ms.subservice: extensibility-integration
 Here's a collection of small code samples on different ways to work with projects.
 
 ## Get project from contained file
-This is how to get the project from one if its files.
+This is how to get the project from one of its files.
 
 ```csharp
  string fileName = "c:\\file\\in\\project.txt";