Remove scope parameter from Logger#tag and Buffer#tag

This reduces the change of a Hash argument being interpreted as keyword
argument inadvertently and clarifies the interface. If a resolver scope
is required, you can also call

    delayed_tag = ->{ |request| request.host }
    logger.tags.merge!(delayed_tag, scope: request)

lib/rackstash/buffer.rb

@@ -263,15 +263,11 @@ module Rackstash
     # @param new_tags [Array<#to_s, #call>] Strings to add as tags to the buffer.
     #   You can either give (arrays of) strings here or procs which return
     #   a string or an array of strings when called.
-    # @param scope [nil, Object] If anything other then `nil` is given here, we
-    #   will evaluate any procs given in the tags in the context of this
-    #   object. If `nil` is given (the default) the procs are directly called
-    #   in the context where they were created.
     # @return [Fields::Tags] the resolved tags which are set on the buffer.
     #   All strings are frozen.
-    def tag(*new_tags, scope: nil)
+    def tag(*new_tags)
       timestamp
-      tags.merge!(new_tags, scope: scope)
+      tags.merge!(new_tags)
     end
 
     # @return [Fields::Tags] a tags list containing the defined tags for the

lib/rackstash/logger.rb

@@ -187,8 +187,8 @@ module Rackstash
     end
 
     # (see Buffer#tag)
-    def tag(*new_tags, scope: nil)
-      buffer.tag(*new_tags, scope: scope)
+    def tag(*new_tags)
+      buffer.tag(*new_tags)
     end
 
     # (see Buffer#tags)

lib/rackstash/rack/middleware.rb

@@ -246,7 +246,7 @@ module Rackstash
           scope: request,
           force: false
         ) unless @request_fields.nil?
-        @logger.tag(@request_tags, scope: request) unless @request_tags.nil?
+        @logger.tags.merge!(@request_tags, scope: request) unless @request_tags.nil?
       end
 
       # @param env [Hash] the Rack environment
@@ -285,7 +285,7 @@ module Rackstash
           force: false
         ) unless @response_fields.nil?
 
-        @logger.tag(@response_tags, scope: headers) unless @response_tags.nil?
+        @logger.tags.merge!(@response_tags, scope: headers) unless @response_tags.nil?
       end
 
       # @param env [Hash] The Rack environment

spec/rackstash/buffer_spec.rb

@@ -486,12 +486,12 @@ RSpec.describe Rackstash::Buffer do
       }
 
       it 'expands single-value proc objects' do
-        buffer.tag(-> { self }, scope: object)
+        buffer.tag(-> { object })
         expect(buffer.tags).to contain_exactly('Hello')
       end
 
       it 'expands multi-value proc objects' do
-        buffer.tag(-> { [[self, 'foobar'], 123] }, scope: object)
+        buffer.tag(-> { [[object, 'foobar'], 123] })
         expect(buffer.tags).to contain_exactly('Hello', 'foobar', '123')
       end
     end