Update get_document.js (#335)

We get the snapshot of data using 'getDoc()' and get result 'docSnap'
And then we perform check on this 'docSnap' in the if else block
So in the else block the comment should ne docSnap.data() will ne undefined

Author: Shabbirjodhpur

firestore-next/test.firestore.js

@@ -583,7 +583,7 @@ describe("firestore", () => {
             if (docSnap.exists()) {
               console.log("Document data:", docSnap.data());
             } else {
-              // doc.data() will be undefined in this case
+              // docSnap.data() will be undefined in this case
               console.log("No such document!");
             }
             // [END get_document]

snippets/firestore-next/test-firestore/get_document.js

@@ -13,7 +13,7 @@ const docSnap = await getDoc(docRef);
 if (docSnap.exists()) {
   console.log("Document data:", docSnap.data());
 } else {
-  // doc.data() will be undefined in this case
+  // docSnap.data() will be undefined in this case
   console.log("No such document!");
 }
 // [END get_document_modular]