expexts changed to expects (#522)

Typo in argument to JACOBIAN_ERROR DimensionMismatch

Author: jwscook

src/jacobian.jl

@@ -197,7 +197,7 @@ end
     return result
 end
 
-const JACOBIAN_ERROR = DimensionMismatch("jacobian(f, x) expexts that f(x) is an array. Perhaps you meant gradient(f, x)?")
+const JACOBIAN_ERROR = DimensionMismatch("jacobian(f, x) expects that f(x) is an array. Perhaps you meant gradient(f, x)?")
 
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