NavLink fails on urls with special characters in them.

[codeviking]

Appears to impact react-router versions 4 and above.

Test Case

https://codepen.io/thecodeviking/pen/KogaJR

Steps to reproduce

1. Create a <NavLink />.
2. Set the to to a value that includes (*).
3. Notice that things don't render as expected.

Expected Behavior

To see a nice, shiny <NavLink />!

Actual Behavior

An exception is thrown:

react-router-dom.js:4100 Uncaught SyntaxError: Invalid regular expression: /^\/paper\/Extended-Symptom-Code-((?:*))-the-Extended-Sympto\/1(?:\/(?=$))?(?=\/|$)/: Nothing to repeat
    at new RegExp (<anonymous>)
    at tokensToRegExp (VM3961 react-router-dom.js:4100)
    at stringToRegexp (VM3961 react-router-dom.js:4028)
    at pathToRegexp (VM3961 react-router-dom.js:4131)
    at compilePath (VM3961 react-router-dom.js:4150)
    at matchPath (VM3961 react-router-dom.js:4179)
    at Route.computeMatch (VM3961 react-router-dom.js:4285)
    at new Route (VM3961 react-router-dom.js:4254)
    at constructClassInstance (VM3960 react-dom.development.js:6897)
    at updateClassComponent (VM3960 react-dom.development.js:8381)

[timdorr]

Already fixed in #5596