Fixed typo in README.asciidoc

Author: Sanders Kleinfeld

README.asciidoc

@@ -1,6 +1,6 @@
 === HTMLBook
 
-Let's write books in HTML! HTMLBook is an open HTML5-based XML standard for the authoring and production of both print and digital books. HTMLBook is built on the following premises::
+Let's write books in HTML! HTMLBook is an open HTML5-based XML standard for the authoring and production of both print and digital books. HTMLBook is built on the following premises:
 
 * Books are timeless. The basic "book" structure has persisted for hundreds of years and will continue to persist for our lifetimes, be it in digital or print form. 
 * HTML is the markup language of the world for the foreseeable future.
@@ -48,4 +48,4 @@ Alternatively, to validate in a GUI XML editor like oXygen, add a +xsi:schemaLoc
 
 * In the coming months, we will be adding additional tools to the HTMLBook project for authoring and producing books with HTMLBook: CSS stylesheets, scripts for generating EPUB/Mobi, etc.
 
-* If you would like to contribute to the HTMLBook project, send us a pull request!
+* If you would like to contribute to the HTMLBook project, send us a pull request!