Update navigation.php
Update navigation.php

See issue #871 (is_single returns true for attachment page (navigation.php))
Schploople/ryanjp-website,Negative-Network/FoundationPress,chirilo/FoundationPress,mevrgior/foundationpress,circleb/SustainLife,linuxbastard/FoundationPress,olefredrik/FoundationPress,derweili/WAYT-WordPress-Themes,zeppytoh/cruorgsg-fp,LepusSorbas/FoundationPress,skoldin/FoundationPress,Schploople/ryanjp-website,randmanrjr/FoundationPress-randman,bellatl/FoundationPress,scordes11/rachel-site,namilwaukee/FoundationPress,Schploople/ryanjp-website,adamfeuer/FoundationPress,philipptrenz/wkkv_theme,codenamesrk/WP-Starter,ozunaj/JaredPress,Digio86/artena,tompepper/tp-foundationpress,derweili/WAYT-WordPress-Themes,zeppytoh/cruorgsg-fp,rollandwalsh/popart,circleb/SustainLife,philipptrenz/wkkv_theme,kateloschinina/KiRa,Negative-Network/FoundationPress,tvnweb/Euroma2017,skoldin/FoundationPress,bellatl/FoundationPress,olefredrik/FoundationPress,ozunaj/JaredPress,Digio86/artena,codenamesrk/WP-Starter,LepusSorbas/FoundationPress,linuxbastard/FoundationPress,colin-marshall/FoundationPress,chirilo/FoundationPress,rollandwalsh/popart,davenaylor/FoundationPress,kateloschinina/KiRa,adamfeuer/FoundationPress,colin-marshall/FoundationPress,tvnweb/Euroma2017,davenaylor/FoundationPress,tompepper/tp-foundationpress,derweili/WAYT-WordPress-Themes,namilwaukee/FoundationPress,randmanrjr/FoundationPress-randman,mevrgior/foundationpress,rollandwalsh/popart,rollandwalsh/popart,scordes11/rachel-site,Digio86/artena,Digio86/artena