fix: do not mutate matcher object message

This made 3 of the assertion tests fail when re-running
as Sinon's spy formatter changed the exports of the
samsam module

lib/sinon/spy-formatters.js

@@ -14,13 +14,14 @@ var slice = arrayProto.slice;
 
 function colorSinonMatchText(matcher, calledArg, calledArgMessage) {
     var calledArgumentMessage = calledArgMessage;
+    var matcherMessage = matcher.message;
     if (!matcher.test(calledArg)) {
-        matcher.message = color.red(matcher.message);
+        matcherMessage = color.red(matcher.message);
         if (calledArgumentMessage) {
             calledArgumentMessage = color.green(calledArgumentMessage);
         }
     }
-    return `${calledArgumentMessage} ${matcher.message}`;
+    return `${calledArgumentMessage} ${matcherMessage}`;
 }
 
 function colorDiffText(diff) {

test/spy-formatters-test.js

@@ -0,0 +1,22 @@
+'use strict'
+const {D} = require('./../lib/sinon/spy-formatters')
+const sinon = require('../lib/sinon')
+const {assert} = require('@sinonjs/referee')
+
+describe('formatter specifier "D"', function () {
+    it('should not mutate matchers passed as arguments', function () {
+        const matcher = sinon.match(function            test() {
+                return false
+            }, 'something'
+        )
+        assert.equals(matcher.message, 'something')
+
+        const stub = sinon.stub()
+
+        stub(1,2,3)
+        /* eslint-disable new-cap */
+        D(stub, [matcher])
+
+        assert.equals(matcher.message, 'something')
+    });
+});