Clean differences from your rake db:structure:dump - it seems to work for 9.4, 9.5 and 9.6

db-structure-clean.rake

# frozen_string_literal: true
namespace :db do
  namespace :structure do

    STRUCTURE_PATH = 'db/structure.sql'

    def clean_structure_file
      original = File.read(STRUCTURE_PATH)
      cleaned = original.dup

      # trailing whitespace
      cleaned.gsub!(/ +$/, '')

      # last line
      cleaned.gsub!(/\n+\Z/, "\n")

      # postgresql 9.5 dumps the row lock status
      cleaned.gsub!(/SET row_security = off;\n/, "")

      # postgresql 9.6 dumps the idle transaction timeout
      cleaned.gsub!(/SET idle_in_transaction_session_timeout = 0;\n/, "")

      # postgresql 9.5 dumps its details
      cleaned.gsub!(/\-\- Dumped from database version 9\.\d\.\d\n\-\- Dumped by pg_dump version 9.\d.\d\n\n/, "")

      # postgresql 9.5 doesn't show empty Tablespace
      cleaned.gsub!(/\-\- Name: ([A-Za-z0-9_ ]+); Type: (TABLE|CONSTRAINT|INDEX); Schema: public; Owner: \-$/) do |_|
        "-- Name: #{$1}; Type: #{$2}; Schema: public; Owner: -; Tablespace:"
      end

      # postgresql 9.6 shows the table and the name
      cleaned.gsub!(/\-\- Name: ([A-Za-z0-9_]+) ([A-Za-z0-9_]+);/) do |_|
        if $1 == "EXTENSION"
          "-- Name: #{$1} #{$2};"
        else
          "-- Name: #{$2};"
        end
      end

      # postgresql 9.5 puts a space here
      cleaned.gsub!(/SET search_path TO "\$user", public;/, "SET search_path TO \"$user\",public;")

      # postgresql 9.6 quotes the position field
      cleaned.gsub!(/"position" integer,/, "position integer,")

      return if original == cleaned

      File.open(STRUCTURE_PATH, 'w') do |f|
        f.write(cleaned)
      end
    end

    Rake::Task['dump'].enhance do
      clean_structure_file
    end

    desc "clean the structure.sql file"
    task :clean do
      clean_structure_file
    end
  end
end

also added this in the beginning:

      # use LF only for new lines
      cleaned.gsub!(/\r\n?/,"\n")

and to also ignore 10.1 versions

      # postgresql 9.5 dumps its details
      cleaned.gsub!(/\-\- Dumped from database version (9|10)\.\d+(\.\d+)?\n\-\- Dumped by pg_dump version (9|10).\d+(.\d+)?\n\n/, "")