doc: it’s -> its in api/child_process.md

PR-URL: https://github.com/nodejs/node/pull/10090
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/child_process.md

@@ -278,7 +278,7 @@ allows messages to be passed back and forth between the parent and child. See
 
 It is important to keep in mind that spawned Node.js child processes are
 independent of the parent with exception of the IPC communication channel
-that is established between the two. Each process has it's own memory, with
+that is established between the two. Each process has its own memory, with
 their own V8 instances. Because of the additional resource allocations
 required, spawning a large number of child Node.js processes is not
 recommended.