Mention required min. version of lessc (#7031)

INSTALL

@@ -63,7 +63,8 @@ INSTALLATION
 5. Point your browser to http://url-to-roundcube/installer/
 6. Follow the instructions of the install script (or see MANUAL CONFIGURATION)
 7. After creating and testing the configuration, remove the installer directory
-8. If you use git sources compile css files for the Elastic skin:
+8. If you use git sources compile css files for the Elastic skin (required
+   lessc >= 1.5.0):
    $ cd skins/elastic
    $ lessc -x styles/styles.less > styles/styles.css
    $ lessc -x styles/print.less > styles/print.css

UPGRADING

@@ -53,7 +53,8 @@ it on a unix system, you need to do the following operations by hand:
    - run `php composer.phar install --no-dev`.
 4c. If you use git sources or the release package without dependencies
    update javascript dependencies by executing `bin/install-jsdeps.sh` script.
-4d. If you use git sources compile css files for the Elastic skin:
+4d. If you use git sources compile css files for the Elastic skin (required
+   lessc >= 1.5.0):
    $ cd skins/elastic
    $ lessc -x styles/styles.less > styles/styles.css
    $ lessc -x styles/print.less > styles/print.css

skins/elastic/README.md

@@ -28,7 +28,7 @@ INSTALLATION
 ------------
 
 All styles are written using LESS syntax. Thus it needs to be compiled
-using the `lessc` command line tool. This comes with the `nodejs-less`
+using the `lessc` (>= 1.5.0) command line tool. This comes with the `nodejs-less`
 RPM package which depends on nodejs.
 ```
     $ lessc -x styles/styles.less > styles/styles.css