Drop Nikola sponsor mention from Readme (#14290)

README.md

@@ -40,7 +40,7 @@ Project Status
 
 Within a major version, language features won't be removed or changed in any way that could prevent a Crystal program written with that version from compiling and working. The built-in standard library might be enriched, but it will always be done with backwards compatibility in mind.
 
-Development of the Crystal language is possible thanks to the community's effort and the continued support of [84codes](https://www.84codes.com/), [Nikola Motor Company](https://nikolamotor.com/) and every other [sponsor](https://crystal-lang.org/sponsors).
+Development of the Crystal language is possible thanks to the community's effort and the continued support of [84codes](https://www.84codes.com/) and every other [sponsor](https://crystal-lang.org/sponsors).
 
 Installing
 ----------