Update journal-of-marketing.csl

From the style guide: "If an author appears more than once
, substitute three em dashes (this will appear as a
one-inch line when typeset) for each author's name"

Moreover, I checked the <a href="http://journals.ama.org/doi/pdf/10.1509/jm.12.0442">a current article</a> where all cases appear: 
```
Anderson, Erin (1985), “The Salesperson as Outside Agent or
Employee: A Transaction Cost Analysis,”
Marketing Science
,
27 (1), 70–84.
——— and Anne T. Coughlan (2002), “Channel Management:
Structure, Governance, and Relationship Management,” in
Handbook of Marketing
, Barton A. Weitz and Robin Wensley,
eds. London: Sage Publications.
———, ———, Adel El-Ansary, and Louis W. Stern (2001),
Mar-
keting Channels
. Upper Saddle River, NJ: Prentice Hall.
——— and Sandy Jap (2005), “The Dark Side of Close Relation-
ships,”
MIT Sloan Management Review
, 46 (3), 75–82.
——— and Barton Weitz (1992), “The Use of Pledges to Build and
Sustain Commitment in Distribution Channels,”
Journal of
Marketing Research
, 29 (February), 18–34.
```
Update journal-of-marketing.csl
Merge pull request #1131 from zuphilip/fix-marketing

Update journal-of-marketing.csl