fix: Fix no-assigning-return-values no callee exception (fixes #8)

Author: randing89

lib/rules/no-assigning-return-values.js

@@ -40,6 +40,9 @@ function isCypressCommandDeclaration(declarator) {
 
   while (object.callee) {
     object = object.callee.object;
+    if (!object) {
+      return;
+    }
   }
 
   return object.name === 'cy';

tests/lib/rules/no-assigning-return-values.js

@@ -14,6 +14,7 @@ ruleTester.run('no-assigning-return-values', rule, {
     { code: 'let foo = true;', parserOptions },
     { code: 'const foo = true;', parserOptions },
     { code: 'const foo = bar();', parserOptions },
+    { code: 'const foo = bar().baz();', parserOptions },
     { code: 'cy.get("foo");', parserOptions },
     { code: 'cy.contains("foo").click();', parserOptions }
   ],