mkrpm honors the '--install-dir' option of grunt

Also, atom.spec now uses the description provided by grunt instead
of hardcoding its own description.

resources/linux/redhat/atom.spec.in

@@ -1,27 +1,27 @@
 Name:           <%= name %>
 Version:        <%= version %>
 Release:        0.1%{?dist}
-Summary:        Atom is a hackable text editor for the 21st century
+Summary:        <%= description %>
 License:        MIT
 URL:            https://atom.io/
 AutoReqProv:    no # Avoid libchromiumcontent.so missing dependency
-Prefix:         /usr/local
+Prefix:         <%= installDir %>
 
 %description
 <%= description %>
 
 %install
-mkdir -p %{buildroot}/usr/local/share/atom
-cp -r Atom/* %{buildroot}/usr/local/share/atom
-mkdir -p %{buildroot}/usr/local/bin/
-ln -sf ../share/atom/resources/app/apm/node_modules/.bin/apm %{buildroot}/usr/local/bin/apm
-cp atom.sh %{buildroot}/usr/local/bin/atom
-chmod 755 %{buildroot}/usr/local/bin/atom
-mkdir -p %{buildroot}/usr/local/share/applications/
-cp atom.desktop %{buildroot}/usr/local/share/applications/
+mkdir -p %{buildroot}/<%= installDir %>/share/atom/
+cp -r Atom/* %{buildroot}/<%= installDir %>/share/atom/
+mkdir -p %{buildroot}/<%= installDir %>/bin/
+ln -sf ../share/atom/resources/app/apm/node_modules/.bin/apm %{buildroot}/<%= installDir %>/bin/apm
+cp atom.sh %{buildroot}/<%= installDir %>/bin/atom
+chmod 755 %{buildroot}/<%= installDir %>/bin/atom
+mkdir -p %{buildroot}/<%= installDir %>/share/applications/
+cp atom.desktop %{buildroot}/<%= installDir %>/share/applications/
 
 %files
-/usr/local/bin/atom
-/usr/local/bin/apm
-/usr/local/share/atom/
-/usr/local/share/applications/atom.desktop
+<%= installDir %>/bin/atom
+<%= installDir %>/bin/apm
+<%= installDir %>/share/atom/
+<%= installDir %>/share/applications/atom.desktop