Use "Environment" instead of "Rscons::Environment" in build tests

build_tests/two_sources/Rsconscript

@@ -1,5 +1,5 @@
 build do
-  Rscons::Environment.new(echo: :command) do |env|
+  Environment.new(echo: :command) do |env|
     env.Object("one.o", "one.c", 'CPPFLAGS' => ['-DONE'])
     env.Program('two_sources.exe', ['one.o', 'two.c'])
   end