[docs] build: update svn url from https:// to svn://

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@15941 3c298f89-4303-0410-b956-a3cf2f4a3e73

docs/build.tex

@@ -45,7 +45,7 @@ This article refers to the "Kamikaze" branch of OpenWrt, which can be downloaded
 subversion using the following command:
 
 \begin{Verbatim}
-$ svn checkout https://svn.openwrt.org/openwrt/trunk kamikaze
+$ svn checkout svn://svn.openwrt.org/openwrt/trunk kamikaze
 \end{Verbatim}
 
 Additionally, there is a trac interface on \href{https://dev.openwrt.org/}{https://dev.openwrt.org/}