Use only single quotes
Modified longDateFormat.LT format 'mm' to 'm'

It's little bit awkward to show 'minutes' in two digits.
So, it need to be modified to show like 2[minute], not 02[minute].
Merge pull request #1800 from kyungw00k/master

@changelog
@section lang-bugfix
@description Use 'm' instead of 'mm' in longDateFormat in korean
Spanish locale: del→de before year

The proper preposition before the year is «de». «del» is used informally for years since 2000 but is not the proper form and cannot be used for years before 2000.
Spanish locale tests: del→de before year
Merge pull request #1804 from rbonvall/develop

Spanish locale: del→de before year

@changelog
@section lang-bugfix
@description del→de before year in spanish
Added meridiem parsing functions for el language
tests added for meridiem parsing for (el) locale
Merge pull request #1812 from nikoskalogridis/master

Add meridiem parsing functions for el language

@changelog
@section lang-bugfix
Improve norwegian bokmål. Fixes #1850

With tests changed.
Merge pull request #1859 from egilkh/develop

Improve norwegian bokmål. Fixes #1850

@changelog
@section lang-bugfix
Add moment.duration.toString()
Merge pull request #1873 from ichernev/feature/duration-to-string

Add moment.duration.toString()

@changelog
@section bugfix