enable log by default to not break existing users

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
diff --git a/Cargo.toml b/Cargo.toml
index fa51394..f5459ea 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,6 +24,7 @@
 publish = false
 
 [features]
+default = ["log"]
 log = ["tracing/log"]
 
 [dependencies]