Fix trivial spelling mistake in docs

doc/release-notes.xml

@@ -446,7 +446,7 @@ xlink:href='http://nixos.org/releases/nix/nix-0.10/'>Nix
   <literal>stdenv</literal>; the formed changes the C compiler, and
   the latter adds additional packages to the front of
   <literal>stdenv</literal>’s initial <envar>PATH</envar>, allowing
-  tools to be overriden.</para>
+  tools to be overridden.</para>
 
   <para>For instance, the package <varname>strategoxt</varname>
   doesn’t build with the GNU Make in <literal>stdenv</literal>

doc/stdenv.xml

@@ -56,7 +56,7 @@ details.)</para>
 <para>Often it is necessary to override or modify some aspect of the
 build.  To make this easier, the standard environment breaks the
 package build into a number of <emphasis>phases</emphasis>, all of
-which can be overriden or modified individually: unpacking the
+which can be overridden or modified individually: unpacking the
 sources, applying patches, configuring, building, and installing.
 (There are some others; see <xref linkend="ssec-stdenv-phases"/>.)
 For instance, a package that doesn’t supply a makefile but instead has
@@ -233,7 +233,7 @@ specific parts of the build (e.g., unpacking the sources or installing
 the binaries).  Furthermore, it allows a nicer presentation of build
 logs in the Nix build farm.</para>
 
-<para>Each phase can be overriden in its entirety either by setting
+<para>Each phase can be overridden in its entirety either by setting
 the environment variable
 <varname><replaceable>name</replaceable>Phase</varname> to a string
 containing some shell commands to be executed, or by redefining the

nixos/doc/manual/configuration.xml

@@ -873,7 +873,7 @@ Any package in Nixpkgs that depends on <literal>emacs</literal> will
 be passed your customised instance.  (However, the value
 <literal>pkgs.emacs</literal> in
 <varname>nixpkgs.config.packageOverrides</varname> refers to the
-original rather than overriden instance, to prevent an infinite
+original rather than overridden instance, to prevent an infinite
 recursion.)</para>
 
 </section>