fix: change default binding of filelines to FL. (#1400)

Author: rzvxa

doc/NERDTree.txt

@@ -287,7 +287,7 @@ I........Toggle whether hidden files displayed......................|NERDTree-I|
 f........Toggle whether the file filters are used...................|NERDTree-f|
 F........Toggle whether files are displayed.........................|NERDTree-F|
 B........Toggle whether the bookmark table is displayed.............|NERDTree-B|
-L........Toggle whether the number of lines in files is displayed...|NERDTree-L|
+L........Toggle whether the number of lines in files is displayed..|NERDTree-FL|
 
 q........Close the NERDTree window..................................|NERDTree-q|
 A........Zoom (maximize/minimize) the NERDTree window...............|NERDTree-A|
@@ -603,8 +603,8 @@ Applies to: no restrictions.
 Toggles whether the bookmarks table is displayed.
 
 ------------------------------------------------------------------------------
-                                                                    *NERDTree-L*
-Default key: L
+                                                                   *NERDTree-FL*
+Default key: FL
 Map setting: *NERDTreeMapToggleFileLines*
 Applies to: no restrictions.
 
@@ -1080,7 +1080,7 @@ Default: 0.
 If this setting is set to 1 then the NERDTree shows number of lines for each
 file.
 
-This setting can be toggled dynamically, per tree, with the |NERDTree-L|
+This setting can be toggled dynamically, per tree, with the |NERDTree-FL|
 mapping.
 Use one of the follow lines for this setting: >
     let NERDTreeShowFilesLines=0

plugin/NERD_tree.vim

@@ -131,7 +131,7 @@ let g:NERDTreeMapToggleBookmarks = get(g:, 'NERDTreeMapToggleBookmarks', 'B')
 let g:NERDTreeMapToggleFiles     = get(g:, 'NERDTreeMapToggleFiles',     'F')
 let g:NERDTreeMapToggleFilters   = get(g:, 'NERDTreeMapToggleFilters',   'f')
 let g:NERDTreeMapToggleHidden    = get(g:, 'NERDTreeMapToggleHidden',    'I')
-let g:NERDTreeMapToggleFileLines = get(g:, 'NERDTreeMapToggleFileLines', 'L')
+let g:NERDTreeMapToggleFileLines = get(g:, 'NERDTreeMapToggleFileLines', 'FL')
 let g:NERDTreeMapToggleZoom      = get(g:, 'NERDTreeMapToggleZoom',      'A')
 let g:NERDTreeMapUpdir           = get(g:, 'NERDTreeMapUpdir',           'u')
 let g:NERDTreeMapUpdirKeepOpen   = get(g:, 'NERDTreeMapUpdirKeepOpen',   'U')