Fix reference to renamed pin/unpin option (#64)

`options[:provider]` was renamed to `options[:from]`

Author: hudon

lib/importmap/commands.rb

@@ -31,7 +31,7 @@ def pin(*packages)
         end
       end
     else
-      puts "Couldn't find any packages in #{packages.inspect} on #{options[:provider]}"
+      puts "Couldn't find any packages in #{packages.inspect} on #{options[:from]}"
     end
   end
 
@@ -53,7 +53,7 @@ def unpin(*packages)
         end
       end
     else
-      puts "Couldn't find any packages in #{packages.inspect} on #{options[:provider]}"
+      puts "Couldn't find any packages in #{packages.inspect} on #{options[:from]}"
     end
   end