Undefined symbols from Crashlytics during build

[rick-cape]

Describe the bug
Since updating to 2.0.5, I'm unable to build on iOS due to an undefined symbol. Could it be missing the Crashlytics framework dependency? Related to #874?

To Reproduce
Steps to reproduce the behavior:
Add cordova-plugin-firebase v2.0.5 to the project, and build on iOS.

Expected behavior
Successfully build.

Example build output:
[11:58:35]: ▸ ❌ Undefined symbols for architecture armv7
[11:58:35]: ▸ > Symbol: OBJC_CLASS$_Crashlytics
[11:58:35]: ▸ > Referenced from: objc-class-ref in FirebasePlugin.o

Plugin Version
app-entitlements 0.0.0 "AppEntitlements"
branch-cordova-sdk 2.6.24 "branch-cordova-sdk"
cordova-fabric-plugin 1.1.14-dev "cordova-fabric-plugin"
cordova-plugin-advanced-http 1.11.1 "Advanced HTTP plugin"
cordova-plugin-android-permissions 1.0.0 "Permissions"
cordova-plugin-app-version 0.1.9 "AppVersion"
cordova-plugin-appavailability 0.4.2 "AppAvailability"
cordova-plugin-apprate 1.4.0 "AppRate"
cordova-plugin-badge 0.8.7 "Badge"
cordova-plugin-device 1.1.7 "Device"
cordova-plugin-dialogs 1.3.4 "Notification"
cordova-plugin-email-composer 0.8.15 "EmailComposer"
cordova-plugin-file 6.0.1 "File"
cordova-plugin-file-transfer 1.7.1 "File Transfer"
cordova-plugin-firebase 1.0.5 "Google Firebase Plugin"
cordova-plugin-globalization 1.11.0 "Globalization"
cordova-plugin-googleplus 5.3.2 "Google SignIn"
cordova-plugin-inappbrowser 1.7.2 "InAppBrowser"
cordova-plugin-ionic-webview 1.2.1 "cordova-plugin-ionic-webview"
cordova-plugin-nativestorage 2.3.2 "NativeStorage"
cordova-plugin-screen-orientation 2.0.2 "Screen Orientation"
cordova-plugin-splashscreen 4.1.0 "Splashscreen"
cordova-plugin-statusbar 2.4.2 "StatusBar"
cordova-plugin-twilio-video-v2preview 1.0.7 "Twilio video conversation plugin"
cordova-plugin-whitelist 1.3.3 "Whitelist"
cordova-plugin-x-socialsharing 5.4.1 "SocialSharing"
cordova-sms-plugin 0.1.13 "Cordova SMS Plugin"
es6-promise-plugin 4.2.2 "Promise"
ionic-plugin-keyboard 2.2.1 "Keyboard"

Desktop (please complete the following information):

• OS: MacOS
• Browser: N/A
• Version: N/A

Smartphone (please complete the following information):
N/A

Additional context
Not much context to add here...other than the fact that this may not be new to 2.0.5, it may have started as early as 2.0.3.