Add explicit type to source blocks in 2-contributing.asc

Author: crd

book/06-github/sections/2-contributing.asc

@@ -305,7 +305,7 @@ The first really useful GitHub specific Markdown feature, especially for use in
 
 You can create a task list like this:
 
-[source]
+[source,text]
 ----
 - [X] Write the code
 - [ ] Write all the tests
@@ -334,7 +334,7 @@ You can also add code snippets to comments. This is especially useful if you wan
 
 To add a snippet of code you have to ``fence'' it in backticks.
 
-[source]
+[source,text]
 ----
 ```java
 for(int i=0 ; i < 5 ; i++)
@@ -356,7 +356,7 @@ If you're responding to a small part of a long comment, you can selectively quot
 
 The quotes look something like this:
 
-[source]
+[source,text]
 ----
 > Whether 'tis Nobler in the mind to suffer
 > The Slings and Arrows of outrageous Fortune,
@@ -380,7 +380,7 @@ image::images/markdown-06-emoji-complete.png[Emoji autocompleter]
 
 Emojis take the form of `:<name>:` anywhere in the comment. For instance, you could write something like this:
 
-[source]
+[source,text]
 ----
 I :eyes: that :bug: and I :cold_sweat:.