fix typo (#3388)

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/context/ids/DistributedTraceId.java

@@ -24,7 +24,7 @@ import org.apache.skywalking.apm.network.language.agent.*;
 /**
  * The <code>DistributedTraceId</code> presents a distributed call chain.
  * <p>
- * This call chain has an unique (service) entrance,
+ * This call chain has a unique (service) entrance,
  * <p>
  * such as: Service : http://www.skywalking.com/cust/query, all the remote, called behind this service, rest remote,
  * db executions, are using the same <code>DistributedTraceId</code> even in different JVM.

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/context/trace/ExitSpan.java

@@ -23,7 +23,7 @@ import org.apache.skywalking.apm.agent.core.context.tag.AbstractTag;
 import org.apache.skywalking.apm.network.trace.component.Component;
 
 /**
- * The <code>ExitSpan</code> represents a service consumer point, such as Feign, Okhttp client for a Http service.
+ * The <code>ExitSpan</code> represents a service consumer point, such as Feign, Okhttp client for an Http service.
  *
  * It is an exit point or a leaf span(our old name) of trace tree. In a single rpc call, because of a combination of
  * discovery libs, there maybe contain multi-layer exit point:

oap-server/server-receiver-plugin/receiver-proto/src/main/proto/google/api/http.proto

@@ -110,7 +110,7 @@ message Http {
 //     }
 //
 //
-// This enables a HTTP JSON to RPC mapping as below:
+// This enables an HTTP JSON to RPC mapping as below:
 //
 // HTTP | RPC
 // -----|-----