small fix in README.txt

Signed-off-by: Chris Cormack <crc@liblime.com>
Signed-off-by: Joshua Ferraro <jmf@liblime.com>

README.txt

@@ -53,7 +53,7 @@ Default installation instructions:
 2. make
 3. sudo make install
 4. ln -s /usr/share/koha/etc/koha-httpd.conf /etc/apache2/sites-available/koha
-5. a2enmod enable rewrite
+5. a2enmod rewrite
 6. a2ensite koha && /etc/init.d/apache2 reload
 7. zebrasrv -c /usr/share/koha/etc/koha-conf.xml
 8. Browse to http://servername:8080/ and answer the questions