Update READMEs with embedme

Author: jtpio

advanced/server-extension/README.md

@@ -559,7 +559,7 @@ setup_args = dict(
     cmdclass= cmdclass,
     packages=setuptools.find_packages(),
     install_requires=[
-        "jupyterlab>=3.0.0rc0,==3.*",
+        "jupyterlab>=3.0.0rc2,==3.*",
     ],
     zip_safe=False,
     include_package_data=True,

basics/hello-world/README.md

@@ -95,7 +95,7 @@ package is declared in the file `package.json`:
 
 },
 "dependencies": {
-  "@jupyterlab/application": "^3.0.0-rc.0"
+  "@jupyterlab/application": "^3.0.0-rc.2"
 ```
 
 With this basic import setup, you can move on to construct a new instance

main-menu/README.md

@@ -89,8 +89,8 @@ After the execution of that command, `package.json` should list them in the
 
 },
 "dependencies": {
-  "@jupyterlab/application": "^3.0.0-rc.0",
-  "@jupyterlab/mainmenu": "^3.0.0-rc.0",
+  "@jupyterlab/application": "^3.0.0-rc.2",
+  "@jupyterlab/mainmenu": "^3.0.0-rc.2",
   "@lumino/widgets": "^1.14.0"
 ```