Fixing small typo on contributing.md page

The word exponentially is spelled wrong

Change-Id: I91bacfcaf30a284ba781c001d11494977f327681
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1989694
Auto-Submit: Joshua Berenhaus <[email protected]>
Commit-Queue: Darin Fisher <[email protected]>
Reviewed-by: Darin Fisher <[email protected]>
Cr-Commit-Position: refs/heads/master@{#729015}
diff --git a/docs/contributing.md b/docs/contributing.md
index 8247c6a..8c3ce6cf 100644
--- a/docs/contributing.md
+++ b/docs/contributing.md
@@ -111,7 +111,7 @@
 - Conform to the [style guide][cr-styleguide].
 - Include tests.
 - Patches should be a reasonable size to review. Review time often increases
-  expontentially with patch size.
+  exponentially with patch size.
 
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