Added missing word within Type Assertions

Author: aarongreenlee

README.md

@@ -243,7 +243,7 @@ This is a useful way of telling TypeScript what the real type of an expression i
 
 The reason we need to do so in this case is that `getElementById`'s return type is `HTMLElement | null`.
 Put simply, `getElementById` returns `null` when it can't find an element with a given `id`.
-We're assuming that `getElementById` will actually succeed, so we need convince TypeScript of that using the `as` syntax.
+We're assuming that `getElementById` will actually succeed, so we need to convince TypeScript of that using the `as` syntax.
 
 TypeScript also has a trailing "bang" syntax (`!`), which removes `null` and `undefined` from the prior expression.
 So we *could* have written `document.getElementById('root')!`, but in this case we wanted to be a bit more explicit.