Update pyro dep in README.md (#1296)

Summary:
This was overlooked in #1295

Pull Request resolved: #1296

Reviewed By: saitcakmak

Differential Revision: D37743867

Pulled By: Balandat

fbshipit-source-id: 1d462efda1c6cd0d5c533b5c65df7bedf870e707

Author: Balandat

README.md

@@ -57,10 +57,10 @@ Optimization simply use Ax.
 **Installation Requirements**
 - Python >= 3.7
 - PyTorch >= 1.9
-- gpytorch >= 1.6
+- GPyTorch >= 1.6
+- pyro-ppl >= 1.8.0
 - scipy
 - multiple-dispatch
-- pyro-ppl == 1.8.0
 
 
 ##### Installing the latest release