Minimal CMake version is 2.8 not 2.6

doc/installation.html

@@ -53,7 +53,7 @@ <h3 id="downloading">Downloading</h3>
 
 <h3 id="cmake">Building using CMake</h3>
 
-<p>SOCI is configured to build using <a href="http://cmake.org/">CMake</a> system in version 2.6+.</p>
+<p>SOCI is configured to build using <a href="http://cmake.org/">CMake</a> system in version 2.8+.</p>
 
 <p>The build configuration allows to control various aspects of compilation and installation by setting common CMake variables that change behaviour, describe system or control build (see <a href="http://cmake.org/cmake/help/documentation.html">CMake help</a>) as well as SOCI-specific variables described below. All these variables are available regardless of platform or compilation toolset used.</p>