Correct unicode point in some ReadMe

In agnoster, agnoster-mercurial and bobthefish, the wrong unicode character was written.
It was ⭠ U+2B60 now  U+E0A0
Change to the one actually used.

as in bobthefish

    # Powerline glyphs
    set __bobthefish_branch_glyph            \uE0A0

and agnoster(-mercurial)

    if [ $status -gt 0 ]
      set -l branch (command git show-ref --head -s --abbrev |head -n1 2> /dev/null)
      set ref "➦ $branch "
    end
    set branch_symbol \uE0A0
    set -l branch (echo $ref | sed  "s-refs/heads/-$branch_symbol -")
    if [ "$dirty" != "" ]