Update Proj1001.md Fix typo

Author: andra2528

rules/Proj1001.md

@@ -4,7 +4,7 @@ ancestor: Rules
 ---
 
 # Proj1001: Use analyzers for packages
-Some [NuGet](https://www.nuget.org/) packages come with there own/dedicated
+Some [NuGet](https://www.nuget.org/) packages come with their own/dedicated
 Roslyn analyzers; they just contain rules to improve the usage of those packages.
 In order to get the best out of those NuGet packages, their analyzer(s) should
 be used.