Add aspell to the slaves

03:34:32 Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 1.119 sec - in org.nuxeo.ecm.platform.commandline.executor.tests.TestCommands
03:34:32 Running org.nuxeo.ecm.platform.commandline.executor.tests.TestService
03:34:33 main 01:34:33,152 WARN  [CommandLineExecutorComponent] Command not available: aspell (command /usr/bin/aspell not found in system path (descriptor CommandLineDescriptor[name=aspell,enabled=true,available=false,command=/usr/bin/aspell,parameterString=-a --lang=#{lang} --encoding=#{encoding} -H --rem-sgml-check=alt < #{textFile},testParameterString=,winParameterString=<null>,winTestParameterString=,winCommand=C:\Program Files\Aspell\bin\aspell.exe,tester=<null>,readOutput=true,installationDirective=You need to install Aspell in order to use this feature. Please see www.aspell.org.,installErrorMessage=<null>]). You need to install Aspell in order to use this feature. Please see www.aspell.org.)