docs: Fix spec version label in README (#54)

Just a minor README fix following up #46

Signed-off-by: Fabrizio Demaria <fabrizio.f.demaria@gmail.com>

Author: fabriziodemaria

README.md

@@ -15,7 +15,7 @@
 <!-- TODO: update this with the version of the SDK your implementation supports -->
 
   <a href="https://github.com/open-feature/spec/releases/tag/v0.8.0">
-    <img alt="Specification" src="https://img.shields.io/static/v1?label=specification&message=v0.7.0&color=yellow&style=for-the-badge" />
+    <img alt="Specification" src="https://img.shields.io/static/v1?label=specification&message=v0.8.0&color=yellow&style=for-the-badge" />
   </a>
   <!-- x-release-please-start-version -->