Update README.md

Removed link to `1.0.0` release branch

Signed-off-by: Doug Hoard <dhoard@users.noreply.github.com>

Author: dhoard

README.md

@@ -17,8 +17,6 @@ process metrics (e.g., memory and CPU usage).
 
 **Documentation is specific to a release.**
 
-[1.0.0](https://github.com/prometheus/jmx_exporter/tree/release-1.0.0)
-
 [0.20.0](https://github.com/prometheus/jmx_exporter/tree/release-0.20.0)
 
 [0.19.0](https://github.com/prometheus/jmx_exporter/tree/release-0.19.0)