indent following line ending in comma with arrow (#420)

an example here : jason0x43/vim-js-indent#4 (comment)

Author: bounceme

indent/javascript.vim

@@ -63,7 +63,7 @@ let s:skip_expr = "synIDattr(synID(line('.'),col('.'),1),'name') =~ '".s:syng_st
 let s:line_term = '\s*\%(\%(\/\/\).*\)\=$'
 
 " Regex that defines continuation lines, not including (, {, or [.
-let s:continuation_regex = '\%([\\*/.:]\|+\@<!+\|-\@<!-\|\%(<%\)\@<!=\|\W[|&?]\|||\|&&\|[^=]=[^=>].*,\)' . s:line_term
+let s:continuation_regex = '\%([\\*/.:]\|+\@<!+\|-\@<!-\|\%(<%\)\@<!=\|\W[|&?]\|||\|&&\|\%(=>.*\|=\)\@<!=[^=>].*,\)' . s:line_term
 
 let s:one_line_scope_regex = '\%(\<else\>\|=>\)' . s:line_term