grass: use Formula[]

Formula/grass.rb

@@ -43,8 +43,8 @@ class Grass < Formula
   end
 
   def install
-    readline = Formula.factory('readline')
-    gettext = Formula.factory('gettext')
+    readline = Formula["readline"].opt_prefix
+    gettext = Formula["gettext"].opt_prefix
 
     args = [
       "--disable-debug", "--disable-dependency-tracking",
@@ -57,13 +57,13 @@ class Grass < Formula
       "--with-lapack",
       "--with-sqlite",
       "--with-odbc",
-      "--with-geos=#{Formula.factory('geos').opt_prefix}/bin/geos-config",
+      "--with-geos=#{Formula["geos"].opt_prefix}/bin/geos-config",
       "--with-png",
-      "--with-readline-includes=#{readline.opt_prefix}/include",
-      "--with-readline-libs=#{readline.opt_prefix}/lib",
+      "--with-readline-includes=#{readline}/include",
+      "--with-readline-libs=#{readline}/lib",
       "--with-readline",
-      "--with-nls-includes=#{gettext.opt_prefix}/include",
-      "--with-nls-libs=#{gettext.opt_prefix}/lib",
+      "--with-nls-includes=#{gettext}/include",
+      "--with-nls-libs=#{gettext}/lib",
       "--with-nls",
       "--with-freetype",
       "--without-tcltk" # Disabled due to compatibility issues with OS X Tcl/Tk
@@ -78,13 +78,13 @@ class Grass < Formula
     if headless? or build.without? 'wxmac'
       args << "--without-wxwidgets"
     else
-      args << "--with-wxwidgets=#{Formula.factory('wxmac').opt_prefix}/bin/wx-config"
+      args << "--with-wxwidgets=#{Formula["wxmac"].opt_prefix}/bin/wx-config"
     end
 
     args << "--enable-64bit" if MacOS.prefer_64_bit?
     args << "--with-macos-archs=#{MacOS.preferred_arch}"
 
-    cairo = Formula.factory('cairo')
+    cairo = Formula["cairo"]
     args << "--with-cairo-includes=#{cairo.include}/cairo"
     args << "--with-cairo-libs=#{cairo.lib}"
     args << "--with-cairo"
@@ -93,7 +93,7 @@ class Grass < Formula
     args << "--with-postgres" if build.with? "postgresql"
 
     if build.with? "mysql"
-      mysql = Formula.factory('mysql')
+      mysql = Formula["mysql"]
       args << "--with-mysql-includes=#{mysql.include}/mysql"
       args << "--with-mysql-libs=#{mysql.lib}"
       args << "--with-mysql"