Fix capitalization, typo, and grammar mistake (parse-community#2533)

* Fix capitalization, typo, and grammar mistake

* fix two typos.

2.3.0.md

@@ -1,6 +1,6 @@
 # Upgrading Parse Server to version 2.3.0
 
-Parse Server version 2.3.0 begins using unique indexes to ensure User's username and email are unique. This is not a backwards incompatable change, but it may in some cases cause a significant performance regression until the index finishes building. Building the unique index before upgrading your Parse Server version will eliminate the performance impact, and is a recommended step before upgrading any app to Parse Server 2.3.0. New apps starting with version 2.3.0 do not need to take any steps before beginning their project.
+Parse Server version 2.3.0 begins using unique indexes to ensure the User's username and email are unique. This is not a backwards incompatible change, but it may in some cases cause a significant performance regression until the index finishes building. Building the unique index before upgrading your Parse Server version will eliminate the performance impact, and is a recommended step before upgrading any app to Parse Server 2.3.0. New apps starting with version 2.3.0 do not need to take any steps before beginning their project.
 
 If you are using MongoDB in Cluster or Replica Set mode, we recommend reading Mongo's [documentation on index building](https://docs.mongodb.com/v3.0/tutorial/build-indexes-on-replica-sets/) first. If you are not using these features, you can execute the following commands from the Mongo shell to build the unique index. You may also want to create a backup first.
 
@@ -58,7 +58,7 @@ In this case, you will need to remove the incorrect index. If your app relies on
 
 ## There is already non-unique data in the username or email field
 
-This is possible if you have explicitly set some user's emails to null. If this is bogus data, and those null fields shoud be unset, you can unset the null emails with this command. If your app relies on the difference between null and unset emails, you will need to upgrade your app to treat null and unset emails the same before building the index and upgrading to Parse Server 2.3.0.
+This is possible if you have explicitly set some user's emails to null. If this is bogus data, and those null fields should be unset, you can unset the null emails with this command. If your app relies on the difference between null and unset emails, you will need to upgrade your app to treat null and unset emails the same before building the index and upgrading to Parse Server 2.3.0.
 
 ```js
 coll.update({ email: { $exists: true, $eq: null } }, { $unset: { email: '' } }, { multi: true })

src/Adapters/Files/FilesAdapter.js

@@ -12,7 +12,7 @@
 // database adapter.
 
 export class FilesAdapter {
-  /* this method is responsible to store the file in order to be retrived later by it's file name
+  /* This method is responsible to store the file in order to be retrieved later by its file name
    *
    * @param filename the filename to save
    * @param data the buffer of data from the file