Fix bug in exporting types with reverse predicates.

[martinmr]

< > brackets are needed around the type name. They were missing.

Fixes #4856

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This change is 

[pawanrawal]

Is there a test which also tries to import a schema file/mutation with a type that a reverse predicate and then verify that the type definition was correctly updated?

Reviewed 2 of 2 files at r1.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @manishrjain and @martinmr)

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worker/export.go, line 336 at r1 (raw file):

	var builder strings.Builder
	x.Check2(builder.WriteString("\t"))
	// Write < > brackets in reverse predicates or Dgraph won't be able to

Should we also mention in the comment that reverse predicate is never written to data files but is only printed as part of type definition?

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worker/export_test.go, line 195 at r1 (raw file):

	require.Equal(t, 1, len(result.Types))
	t.Logf("result %+v", result.Types)

Why do we only log these and not compare their values?

[martinmr]

There's already a test that exports the schema and loads it back. I just changed the type to include a reverse predicate to trigger the bug.

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @manishrjain and @pawanrawal)

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worker/export.go, line 336 at r1 (raw file):

Previously, pawanrawal (Pawan Rawal) wrote…

Should we also mention in the comment that reverse predicate is never written to data files but is only printed as part of type definition?

Done. Rephrased the comment to make this point.

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worker/export_test.go, line 195 at r1 (raw file):

Previously, pawanrawal (Pawan Rawal) wrote…

Why do we only log these and not compare their values?

Sorry, this change was made during debugging. I have removed this code.

The line right below is doing the comparison.