Fixing ambiguous remark in Preserve inputs' types

This PR is based on the [discussion in the forum](https://discourse.julialang.org/t/not-clear-what-0-01f0x-is-in-the-flux-docs/40553?u=mathematics) on the ambiguity of `0.01f0x` in the line
> While one could change the activation function (e.g. to use `0.01f0x`)

docs/src/performance.md

@@ -39,7 +39,7 @@ E.g. the following will have run into the same problem as above:
     leaky_tanh(x) = 0.01*x + tanh(x)
 ```
 
-While one could change the activation function (e.g. to use `0.01f0x`), the idiomatic (and safe way)  to avoid type casts whenever inputs changes is to use `oftype`:
+While one could change the activation function (e.g. to use `0.01f0*x`), the idiomatic (and safe way)  to avoid type casts whenever inputs changes is to use `oftype`:
 ```
     leaky_tanh(x) = oftype(x/1, 0.01)*x + tanh(x)
 ```