update m4 to 1.4.18

add check method

packages/m4.rb

 require 'package'
 
 class M4 < Package
-  version '1.4.17'
-  source_url 'ftp://ftp.gnu.org/gnu/m4/m4-1.4.17.tar.xz'
-  source_sha1 '74ad71fa100ec8c13bc715082757eb9ab1e4bbb0'
+  version '1.4.18'
+  source_url 'https://ftp.gnu.org/gnu/m4/m4-1.4.18.tar.xz'
+  source_sha1 '228604686ca23f42e48b98930babeb5d217f1899'
 
   depends_on 'libsigsegv'
 
@@ -13,6 +13,10 @@ class M4 < Package
   end
 
   def self.install
-    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install-strip"
+  end
+
+  def self.check
+    system "make check"
   end
 end