Fix grammar in BaseMeter#transform javadoc (#838)

Author: zh-hanlabs

apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/meter/BaseMeter.java

@@ -55,7 +55,7 @@ public String getTag(String tagKey) {
 
     /**
      * Transform the meter to gRPC message bean
-     * @return if dont need to transform or no changed, return null to ignore
+     * @return if no transformation is needed or nothing has changed, return null to ignore
      */
     public abstract MeterData.Builder transform();