ref-manual: Fixed title name in link.

The actual title of the sdk-manual does not include the word
"Manual".  So, the reference to the book should terminate with the
word "manual" in lower case.

(From yocto-docs rev: 41bc85776f0b172fc243b6e5a5ca13b72e8399e5)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-devtool-reference.xml

@@ -474,7 +474,7 @@
             workflow in the
             "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-devtool-use-devtool-upgrade-to-create-a-version-of-the-recipe-that-supports-a-newer-version-of-the-software'>Use <filename>devtool upgrade</filename> to Create a Version of the Recipe that Supports a Newer Version of the Software</ulink>"
             section in the Yocto Project Application Development and the
-            Extensible Software Development Kit (eSDK) Manual.
+            Extensible Software Development Kit (eSDK) manual.
             You can also see an example of how to use
             <filename>devtool upgrade</filename> in the
             "<ulink url='&YOCTO_DOCS_DEV_URL;#gs-using-devtool-upgrade'>Using <filename>devtool upgrade</filename></ulink>"