doc: fix a typo in platform-support.md

Author: lasiotus

src/doc/rustc/src/platform-support.md

@@ -431,7 +431,7 @@ target | std | host | notes
 `x86_64-unknown-l4re-uclibc` | ? |  |
 [`x86_64-unknown-linux-none`](platform-support/x86_64-unknown-linux-none.md) | * |  | 64-bit Linux with no libc
 [`x86_64-unknown-managarm-mlibc`](platform-support/managarm.md) | ? |   | x86_64 Managarm
-[`x86_64-unknown-motor`[(platform-support/motor.md) | ? |  | x86_64 Motor OS
+[`x86_64-unknown-motor`](platform-support/motor.md) | ? |  | x86_64 Motor OS
 [`x86_64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 64-bit OpenBSD
 [`x86_64-unknown-trusty`](platform-support/trusty.md) | ✓ |  |
 `x86_64-uwp-windows-gnu` | ✓ |  |