update issue tmpl for baggage (open-telemetry#1100)

Signed-off-by: Andrew Hsu <xuzuan@gmail.com>

Author: andrewhsu

.github/ISSUE_TEMPLATE/correlationcontext.md renamed to .github/ISSUE_TEMPLATE/baggage.md

@@ -1,7 +1,7 @@
 ---
-name: CorrelationContext
-about: Issues related to the specification/correlationcontext directory
-labels: spec:correlationcontext
+name: Baggage
+about: Issues related to the specification/baggage directory
+labels: spec:baggage
 ---
 
 **What are you trying to achieve?**