jedi#show_documentation: do not use quotes around bufname

autoload/jedi.vim

@@ -364,7 +364,7 @@ function! jedi#show_documentation() abort
             silent execute 'sbuffer '.bn
         endif
     else
-        split '__doc__'
+        split __doc__
     endif
 
     setlocal modifiable

test/documentation.vim

@@ -13,7 +13,7 @@ describe 'documentation docstrings'
     it 'simple'
         put = 'ImportError'
         normal GK
-        Expect bufname('%') == "'__doc__'"
+        Expect bufname('%') == "__doc__"
         Expect &filetype == 'rst'
         let content = join(getline(1,'$'), "\n")
         Expect stridx(content, "Import can't find module") > 0