miniconda: update livecheck

The existing `livecheck` block for `miniconda` contains a `#strategy`
call but it doesn't specify a strategy symbol. We expect the symbol to
always be provided when `#strategy` is used but we enforce this using
a RuboCop and the `livecheck` block RuboCops don't apply to casks yet
(I'm currently working on this).

This adds the missing `#strategy` symbol and renames the `strategy`
block argument to use the standard `page` name for `PageMatch`.

Casks/m/miniconda.rb

@@ -13,9 +13,9 @@
 
   livecheck do
     url "https://repo.anaconda.com/miniconda/"
-    strategy do |content|
-      sha256 = content.scan(/>Miniconda3-latest-MacOSX-#{arch}\.sh<.{,99}>(\w{64})</im).first.first
-      content.scan(/>Miniconda3-(py\d+_[\d.-]+)-MacOSX-#{arch}\.sh<.{,99}>#{sha256}</im).first.first
+    strategy :page_match do |page|
+      sha256 = page.scan(/>Miniconda3-latest-MacOSX-#{arch}\.sh<.{,99}>(\w{64})</im).first.first
+      page.scan(/>Miniconda3-(py\d+_[\d.-]+)-MacOSX-#{arch}\.sh<.{,99}>#{sha256}</im).first.first
     end
   end