fix(apm): give users access to raw server responses

We were building server responses if the reply was `null`, which
was only the case for some primitives which we were not passing up
to the porcelain driver.  Now we are doing that, so there should
be no need to hand craft responses.

NODE-1190

lib/apm.js

@@ -516,8 +516,9 @@ var Instrumentation = function(core, options, callback) {
               // Emit the command
               self.emit('failed', command);
             } else {
-              // Do we have a getMore
-              if (commandName.toLowerCase() === 'getmore' && r == null) {
+              if (r && r.documents) {
+                r = r.documents[0];
+              } else if (commandName.toLowerCase() === 'getmore' && r == null) {
                 r = {
                   cursor: {
                     id: cursor.cursorState.cursorId,

yarn.lock

@@ -2110,7 +2110,14 @@ mongodb-core@2.1.17:
 
 mongodb-core@mongodb-js/mongodb-core#3.0.0:
   version "3.0.0-beta1"
-  resolved "https://codeload.github.com/mongodb-js/mongodb-core/tar.gz/d7cd5cdda5fddc8635353063d245fb083ef1d545"
+  resolved "https://codeload.github.com/mongodb-js/mongodb-core/tar.gz/69994597bd354c9945d0f47fe4abfb917448ace1"
+  dependencies:
+    bson "~1.0.4"
+    require_optional "^1.0.1"
+
+mongodb-core@mongodb-js/mongodb-core#causally-consistent-reads:
+  version "3.0.0-beta1"
+  resolved "https://codeload.github.com/mongodb-js/mongodb-core/tar.gz/67b10c1f9175851496f5675ad18171466079dccc"
   dependencies:
     bson "~1.0.4"
     require_optional "^1.0.1"