srmio: modernize autotools deps

Formula/srmio.rb

@@ -9,9 +9,9 @@ class Srmio < Formula
   head do
     url 'https://github.com/rclasen/srmio.git'
 
-    depends_on :autoconf
-    depends_on :automake
-    depends_on :libtool
+    depends_on "autoconf" => :build
+    depends_on "automake" => :build
+    depends_on "libtool" => :build
   end
 
   def install