Update ottrace environment variable to match spec. (open-telemetry#1406)

Author: Anuraag Agrawal

CHANGELOG.md

@@ -14,6 +14,7 @@ New:
 
 Updates:
 
+- Update OT Trace propagator environment variable to match latest name([#1406](https://github.com/open-telemetry/opentelemetry-specification/pull/1406))
 - Remove Metrics SDK specification to avoid confusion, clarify that Metrics API
   specification is not recommended for client implementation
   ([#1401](https://github.com/open-telemetry/opentelemetry-specification/pull/1401))

specification/sdk-environment-variables.md

@@ -39,7 +39,7 @@ Known values for OTEL_PROPAGATORS are:
 - `"b3multi"`: [B3 Multi](https://github.com/openzipkin/b3-propagation#multiple-headers)
 - `"jaeger"`: [Jaeger](https://www.jaegertracing.io/docs/1.21/client-libraries/#propagation-format)
 - `"xray"`: [AWS X-Ray](https://docs.aws.amazon.com/xray/latest/devguide/xray-concepts.html#xray-concepts-tracingheader) (_third party_)
-- `"ottracer"`: [Lightstep](https://github.com/lightstep/lightstep-tracer-java-common/blob/master/common/src/main/java/com/lightstep/tracer/shared/TextMapPropagator.java) (_third party_)
+- `"ottrace"`: [OT Trace](https://github.com/opentracing?q=basic&type=&language=) (_third party_)
 
 Known values for `OTEL_TRACES_SAMPLER` are: