Point README.md to soon-to-be new release

Author: elainethale

README.md

@@ -48,7 +48,7 @@ pip install gdxpds
 or
 
 ```bash
-pip install git+https://github.com/NREL/gdx-pandas.git@v1.1.0
+pip install git+https://github.com/NREL/gdx-pandas.git@v1.2.0
 ```
 
 or