Warning: Variable 'limitLines' was never mutated; consider changing to 'let' constant

When I call Analyse in the Xcode (Product->Analyse) of my project I see several warnings about
`Variable 'limitLines' was never mutated; consider changing to 'let' constant`

## What did you do?
1) Open Xcode;
2) Run Analyse.

## What did you expect to happen?

No warnings

## What happened instead?

I see 8 warnings.

## Charts Environment

**Charts version/Branch/Commit Number:** 3.4.0
**Xcode version:** 11.4
**Swift version:** Swift 5
**Platform(s) running Charts:** Pods
**macOS version running Xcode:** 10.15.4