fastlane: fastlane cert --output_path doesn't generate p12 file

New Issue Checklist

• Updated fastlane to the latest version
• I read the Contribution Guidelines
• I read docs.fastlane.tools
• I searched for existing GitHub issues

Issue Description

mkdir certificates
fastlane cert --output_path certificates 

Complete output when running fastlane, including the stack trace and command used

Only .cer file is generated instead of three files .cer, p12 and certSigningRequest. See https://circleci.com/docs/1.0/ios-code-signing/

I have to upload p12 file to Circle CI which is missing.

Environment

🚫 fastlane environment 🚫

Stack

Key	Value
OS	10.13
Ruby	2.3.1
Bundler?	false
Git	git version 2.10.1
Installation Source	/usr/local/bin/fastlane
Host	Mac OS X 10.13 (17A405)
Ruby Lib Dir	/usr/local/Cellar/ruby/2.3.1_2/lib
OpenSSL Version	OpenSSL 1.0.2j 26 Sep 2016
Is contained	false
Is homebrew	false
Is installed via Fabric.app	false
Xcode Path	/Applications/Xcode.app/Contents/Developer/
Xcode Version	8.3.2

System Locale

Error
No Locale with UTF8 found 🚫

fastlane files:

No Fastfile found

No Appfile found

fastlane gems

Gem	Version	Update-Status
fastlane	2.62.1	🚫 Update available

Loaded fastlane plugins:

No plugins Loaded

Loaded gems

Gem	Version
did_you_mean	1.0.0
slack-notifier	1.5.1
rouge	2.0.7
xcpretty	0.2.8
terminal-notifier	1.8.0
unicode-display_width	1.3.0
terminal-table	1.8.0
plist	3.3.0
public_suffix	2.0.5
addressable	2.5.2
multipart-post	2.0.0
word_wrap	1.0.0
babosa	1.0.2
colored	1.2
highline	1.7.8
commander-fastlane	4.4.5
excon	0.59.0
faraday	0.13.1
unf_ext	0.0.7.4
unf	0.1.4
domain_name	0.5.20170404
http-cookie	1.0.3
faraday-cookie_jar	0.0.6
fastimage	2.1.0
mini_magick	4.5.1
multi_json	1.12.2
multi_xml	0.6.0
rubyzip	1.2.1
security	0.1.3
dotenv	2.2.1
faraday_middleware	0.12.2
uber	0.1.0
declarative	0.0.10
declarative-option	0.1.0
representable	3.0.4
retriable	3.1.1
mime-types-data	3.2016.0521
mime-types	3.1
httpclient	2.8.3
google-api-client	0.13.6
json	2.1.0
io-console	0.4.5
tty-screen	0.5.1
claide	1.0.2
colored2	3.1.2
nanaimo	0.2.3
xcodeproj	1.5.3
bundler	1.15.4

generated on: 2017-11-23