compose: Use 575px  instead of 551px  as breakpoint for mobile.
compose: Use 575px  instead of 551px  as breakpoint for mobile.

This was tested to be working fine. Since display property
doesn't depend upon 551px, no regressions are possible.

hackerkid/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,hackerkid/zulip,andersk/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,kou/zulip,andersk/zulip,andersk/zulip,zulip/zulip,rht/zulip,andersk/zulip,kou/zulip,rht/zulip,andersk/zulip,kou/zulip,rht/zulip,eeshangarg/zulip,hackerkid/zulip,punchagan/zulip,zulip/zulip,punchagan/zulip,punchagan/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,punchagan/zulip,zulip/zulip,rht/zulip,andersk/zulip