Corrected spelling in README.

Author: rickogden

README.md

@@ -53,7 +53,7 @@ The documentation for the current branch can be found [here](https://github.com/
 
 ## Sponsors :heart_eyes: 
 
-We are proudly supported by the following echange rate providers offering *free plans up to 1,000 requests per day*:
+We are proudly supported by the following exchange rate providers offering *free plans up to 1,000 requests per day*:
 
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