Typo fix in doc
Typo fix in doc

"assignment" instead of "assigmnent".
RELNOTES: n/a

Closes #962 from DenrizSusam/closure-library:patch-1

ORIGINAL_AUTHOR=Deniz Susman <susmandeniz@gmail.com>

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google/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,google/closure-library,google/closure-library,google/closure-library,google/closure-library,lucidsoftware/closure-library