Does Eldritch Blast travel in a straight line?

Yes

I'll just add some linguistic corroboration to the wording:

A beam of crackling energy streaks toward a creature within range.

Wordnik defines a beam as:

A ray or shaft of light.

And a ray as:

A narrow stream of radiant energy, especially visible light, traveling in a straight or nearly straight line.

And a streak:

n. A line, mark, smear, or band differentiated by color or texture from its surroundings.

n. An inherent, often contrasting quality.

n. A ray or flash of light.

Plus, if trajectories could be arbitrarily wibbly wobbly, that would impact range calculations and I'm sure most players are not interested in that kind of math.

Cover is concerned with what is between you and your target, nothing more, so it doesn't matter if eldritch blast shoots straight or wibbly wobbly.

The rules for cover state:

Walls, trees, creatures, and other obstacles can provide cover during combat, making a target more difficult to harm. A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.

There are three degrees of cover. If a target is behind multiple sources of cover, only the most protective degree of cover applies; the degrees aren't added together. For example, if a target is behind a creature that gives half cover and a tree trunk that gives three-quarters cover, the target has three-quarters cover.

Cover concerns itself only with what is between the attacker and the target. There is no mention at all about having an additional visual perspective changing the cover rules in any way, nor do the rules for your familiar, so the cover rules apply as normal. Further, eldritch blast makes no mention of ignoring cover, so it does not ignore cover.

Now, if you were to take the feat spell sniper:

Your ranged spell attacks ignore half cover and three-quarters cover,

you could flavor your eldritch blast to curve around cover all you want - and it would actually ignore the cover!

Now, I know the rules are not a real-life simulator, but this is a scenario where the rules and real-life make sense in parallel. Imagine you had a VR head set on your head and you were seeing a birds eye view from a drone flying above you and a friend standing 100 feet apart in a field. You will most certainly be worse at throwing a baseball to your friend, not better.

It should be mentioned that spells only do what they say they do, and eldritch blast makes no mention of interacting with cover any differently than is typical. One such example that does specify an interaction with cover is sacred flame:

Flame-like radiance descends on a creature that you can see within range. The target must succeed on a Dexterity saving throw or take 1d8 radiant damage. The target gains no benefit from cover for this saving throw.

If a spell or ability interacts with cover differently than usual, the description will most certainly let you know.