Correct error in checking for primitive data type

[bruceadowns]

Describe the PR
This PR corrects the error in checking for primitive data type.

Relation issue
Bug introduces in d74ed70.

Additional context
I am seeing this error in the latest build:

$ swag init -g cmd/cnc.go
2019/09/11 11:35:02 Generate swagger docs....
2019/09/11 11:35:02 Generate general API Info, search dir:./
2019/09/11 11:35:02 ParseComment error in file cmd/cnc.go :can not find schema type: "cmd.int"

[codecov-io]

Codecov Report

Merging #516 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #516   +/-   ##
=======================================
  Coverage   86.78%   86.78%           
=======================================
  Files           7        7           
  Lines        1536     1536           
=======================================
  Hits         1333     1333           
  Misses        119      119           
  Partials       84       84

Impacted Files	Coverage Δ
operation.go	92.6% <100%> (ø)	⬆️

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[easonlin404]

I wonder that what cause bug in d74ed70? Any thought? @ubogdan

[ubogdan]

LGTM