Ability Score Increase: Your Dexterity score increases by 2.
Age: Goblins mature faster than humans, reaching adulthood around age 10. A healthy Goblin can live to 50 or more, but rarely does.
Alignment: Goblins tend towards evil; they tend to be greedy, lazy, and selfish. They have no particular inclination towards following orders without a strong incentive to do so, but are happy for someone else to be responsible for hard decisions or dangerous tasks. As a result, they have little inclination towards either law or chaos and their most common alignment is Neutral Evil. Goblins that live among other races are capable of working within a system to get what they want, or ignore it entirely when it is convenient, tending more towards True Neutral or Chaotic Neutral.
Size: Goblins are between 3 and 4 feet tall and average about 35 pounds. Your size is Small.
Speed: You have a base walking speed of 30 feet.
Darkvision: Goblins commonly live underground, and even surface-dwelling Goblins tend to be more active at night, emerging to scavenge or raid and then laying low during daylight hours. You can see in dim light within 60 feet as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.
Languages: You can speak, read, and write Common and Goblin, which uses a crude version of the Dwarvish alphabet. Goblin is rarely written down, except in the form of graffiti which Goblins use to mark their territory and mock their enemies.
Nimble Escape: Goblins favor hit and run tactics, which they use in groups to wear down their opponents while trying to remain out of range. When an opponent targets you with a melee attack and misses, you can take the Disengage action as a reaction to move away from your attacker.
Sneaky: You are proficient in Stealth.
Sniveling: Goblins are used to being treated with contempt by those stronger than they are, which is nearly everyone. The average goblin will shamelessly lie, boot-lick, grovel, and flatter to avoid being swatted down by a boss or foe. Their ancient enemies have long realized that goblins treat mercy as a weakness, but other races either haven't caught on or don't regard goblins as worth the trouble to kill. You have advantage on Charisma checks to avoid being blamed or punished for your actions by anyone other than a Dwarf or an Elf.
Opportunistic Eater: Goblins enthusiastically eat a wide variety of foods that more civilized races turn their noses up at; they also are accustomed to having to provide for themselves in a wide variety of situations. You have advantage on Wisdom (Survival) checks to forage for food, and can forage for food anywhere- including inside dungeons and cities. At the DM's option, the food that you find may not be fit for non-goblinoids to eat!
edit: Thanks to /r/DnD for feedback- I've made a couple adjustments for balance and simplicity that were suggested there and added the 'Sniveling' feature.