Modifies sort function and adds a unit test

lib/ex.coffee

@@ -438,10 +438,19 @@ class Ex
           optionProcessor()
 
   sort: ({ range }) =>
-    range = [[range[0], 0], [range[1] + 1, 0]]
     editor = atom.workspace.getActiveTextEditor()
-    text = editor.getTextInBufferRange(range)
-    sortedText = _.sortBy(text.split(/\n/)).join('\n')
-    editor.buffer.setTextInRange(range, sortedText)
+    sortingRange = [[]]
+    isMultiLine = range[1] - range[0] > 1
+    if isMultiLine
+      sortingRange = [[range[0], 0], [range[1] + 1, 0]]
+    else
+      sortingRange = [[0, 0], [editor.getLastBufferRow(), 0]]
+
+    textLines = []
+    for lineIndex in [sortingRange[0][0]..sortingRange[1][0] - 1]
+      textLines.push(editor.lineTextForBufferRow(lineIndex))
+
+    sortedText = _.sortBy(textLines).join('\n') + '\n'
+    editor.buffer.setTextInRange(sortingRange, sortedText)
 
 module.exports = Ex

spec/ex-commands-spec.coffee

@@ -983,3 +983,13 @@ describe "the commands", ->
       expect(calls.length).toEqual 2
       expect(calls[0].args[0].range).toEqual [0, 2]
       expect(calls[1].args[0].range).toEqual [3, 3]
+
+  desctibe ':sort', ->
+    beforeEach ->
+      editor.setText('ghi\nabc\njkl\ndef\n')
+      editor.setCursorBufferPosition([0, 0])
+
+    it "sorts entire file if range is not multi-line", ->
+      openEx()
+      submitNormalModeInputText('sort')
+      expect(atom.getText()).toEqual('abc\ndef\nghi\njkl\n')