refactor(command): use constant for writeConcer/collation support

Author: mbroadst

lib/operations/command_v2.js

@@ -8,6 +8,8 @@ const WriteConcern = require('../write_concern');
 const maxWireVersion = require('../core/utils').maxWireVersion;
 const commandSupportsReadConcern = require('../core/sessions').commandSupportsReadConcern;
 
+const SUPPORTS_WRITE_CONCERN_AND_COLLATION = 5;
+
 class CommandOperationV2 extends OperationBase {
   constructor(parent, options) {
     super(options);
@@ -42,7 +44,7 @@ class CommandOperationV2 extends OperationBase {
       Object.assign(cmd, { readConcern: this.readConcern });
     }
 
-    if (serverWireVersion >= 5) {
+    if (serverWireVersion >= SUPPORTS_WRITE_CONCERN_AND_COLLATION) {
       if (this.writeConcern && this.hasAspect(Aspect.WRITE_OPERATION)) {
         Object.assign(cmd, { writeConcern: this.writeConcern });
       }