refactor: `Vec::with_capacity(0)` => `vec![]`

`vec![]` also results in a capacity of 0, see
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=184113a9afa945cf3cf3b8f854f4c5ce

trace/src/ctx.rs

@@ -72,7 +72,7 @@ impl SpanContext {
             trace_id: TraceId(NonZeroU128::new(trace_id).unwrap()),
             parent_span_id: None,
             span_id: SpanId(NonZeroU64::new(span_id).unwrap()),
-            links: Vec::with_capacity(0),
+            links: vec![],
             collector: Some(collector),
         }
     }
@@ -85,7 +85,7 @@ impl SpanContext {
                 trace_id: self.trace_id,
                 span_id: SpanId::gen(),
                 collector: self.collector.clone(),
-                links: Vec::with_capacity(0),
+                links: vec![],
                 parent_span_id: Some(self.span_id),
             },
             start: None,

trace_http/src/ctx.rs

@@ -155,7 +155,7 @@ fn decode_b3(
     }
 
     // Links cannot be specified via the HTTP header
-    let links = Vec::with_capacity(0);
+    let links = vec![];
 
     Ok(Some(SpanContext {
         trace_id: required_header(headers, B3_TRACE_ID_HEADER, parse_trace)?,
@@ -216,7 +216,7 @@ fn decode_jaeger(
     }
 
     // Links cannot be specified via the HTTP header
-    let links = Vec::with_capacity(0);
+    let links = vec![];
 
     Ok(Some(SpanContext {
         trace_id: decoded.trace_id,