Update Call to WrenInterpret in Docs

Fixes #599 by updating the arguments to WrenInterpret to match the new
API.

doc/site/embedding/index.markdown

@@ -131,7 +131,9 @@ VM, waiting to run some code!
 You execute a string of Wren source code like so:
 
     :::c
-    WrenInterpretResult result = wrenInterpret(vm,
+    WrenInterpretResult result = wrenInterpret(
+        vm,
+        "my_module",
         "System.print(\"I am running in a VM!\")");
 
 The string is a series of one or more statements separated by newlines. Wren

doc/site/embedding/storing-c-data.markdown

@@ -207,7 +207,7 @@ Over in the host, first we'll set up the VM:
       config.bindForeignMethodFn = bindForeignMethod;
 
       WrenVM* vm = wrenNewVM(&config);
-      wrenInterpret(vm, "some code...");
+      wrenInterpret(vm, "my_module", "some code...");
 
       return 0;
     }