Typo corrections Update CONTRIBUTING.md (#2353)

In the section Adding new dependencies, the sentence "please be sure that is is well-maintained and trustworthy" contains a typo: "is is" corrected to "it is".

docs/CONTRIBUTING.md

@@ -66,7 +66,7 @@ B. Pre-defined configuration:
 ## Adding new dependencies
 For all types of dependencies:
 - **Do not add** a dependency if the desired functionality is easily implementable
-- If adding a dependency is necessary, please be sure that is is well-maintained and trustworthy
+- If adding a dependency is necessary, please be sure that it is well-maintained and trustworthy