Update version to 0.3

Author: lossyrob

README.md

@@ -28,7 +28,7 @@ From source repository:
 To install a specific versions of STAC, install the matching version of pystac.
 
 ```bash
-> pip install pystac==0.2.0
+> pip install pystac==0.3.0
 ```
 
 The table below shows the corresponding versions between pystac and STAC:

docs/index.rst

@@ -10,7 +10,7 @@ Requirements
 STAC Versions
 =============
 
-* 0.2 -> STAC Version 0.8
+* 0.3 -> STAC Version 0.8
 
 Standard pip install
 ====================