Readme: fix USE_COLORS to DEBUG_COLORS

Also remove trailing whitespace

Readme.md

@@ -58,9 +58,9 @@ setInterval(function(){
  ```cmd
  set DEBUG=*,-not_this
  ```
- 
+
  Note that PowerShell using different syntax to set environment variables.
- 
+
  ```cmd
  $env:DEBUG = "*,-not_this"
   ```
@@ -120,13 +120,13 @@ setInterval(function(){
   Colored output looks something like:
 
   ![](https://cloud.githubusercontent.com/assets/71256/3139768/b98c5fd8-e8ef-11e3-862a-f7253b6f47c6.png)
-  
+
 ## Output streams
 
-  
+
 ### stderr vs stdout
   By default `debug` will log to stderr, however this can be changed by setting the environment variable `DEBUG_FD` to `1` for stdout and `2` for stderr (the default value).
-  
+
 You can also set an alternative logging method per-namespace by overriding the `log` method on a per-namespace or globally:
 
 Example _stdout.js_:
@@ -163,10 +163,10 @@ $ DEBUG_FD=3 node your-app.js 3> whatever.log
 
 ### Terminal colors
 
-  By default colors will only be used in a TTY. However this can be overridden by setting the environment variable `USE_COLORS` to `1`. 
-  
-  Note: Certain IDEs (such as WebStorm) don't support colors on stderr. In these cases you must set `USE_COLORS` to `1` and additionally change `DEBUG_FD` to `1`.
-  
+  By default colors will only be used in a TTY. However this can be overridden by setting the environment variable `DEBUG_COLORS` to `1`.
+
+  Note: Certain IDEs (such as WebStorm) don't support colors on stderr. In these cases you must set `DEBUG_COLORS` to `1` and additionally change `DEBUG_FD` to `1`.
+
 ## Authors
 
  - TJ Holowaychuk