change Environment#parse_makefile_deps() to a class method

spec/rscons/environment_spec.rb

@@ -1,6 +1,6 @@
 module Rscons
   describe Environment do
-    describe '.clone' do
+    describe "#clone" do
       it 'should create unique copies of each construction variable' do
         env = Environment.new
         env["CPPPATH"] << "path1"
@@ -11,13 +11,12 @@ module Rscons
       end
     end
 
-    describe '.parse_makefile_deps' do
+    describe ".parse_makefile_deps" do
       it 'handles dependencies on one line' do
         File.should_receive(:read).with('makefile').and_return(<<EOS)
 module.o: source.cc
 EOS
-        env = Environment.new
-        env.parse_makefile_deps('makefile', 'module.o').should == ['source.cc']
+        Environment.parse_makefile_deps('makefile', 'module.o').should == ['source.cc']
       end
 
       it 'handles dependencies split across many lines' do
@@ -26,8 +25,7 @@ module.o: module.c \\
   module.h \\
   other.h
 EOS
-        env = Environment.new
-        env.parse_makefile_deps('makefile', 'module.o').should == [
+        Environment.parse_makefile_deps('makefile', 'module.o').should == [
           'module.c', 'module.h', 'other.h']
       end
     end