Revert "Exec not needed for fish shell"

This reverts commit 5d30b0e105.

README.md

@@ -52,7 +52,7 @@ From inside that directory you can:
     
     **Pyenv note**: You may also need to add `eval "$(pyenv init -)"` to your profile if you haven't done so already.
 
-3. **Restart your shell to enable pyenv-virtualenv (not needed in fish)**
+3. **Restart your shell to enable pyenv-virtualenv**
 
     ```sh
     $ exec "$SHELL"