I've noticed a lot of these exercises in the last several modules I have done give different default values than what are needed for the lesson (specifically in Admin Advanced, but IIRC Admin Intermediate and possibly Developer Beginner also).
 
Instructions for https://trailhead.salesforce.com/trails/force_com_admin_advanced/modules/advanced_formulas/units/picklist_formulas state:

"In Field Label, enter Reason for Escalating. Field Name populates automatically."
 
For the formula given, it says to use

AND(
  ISPICKVAL(Status, "Escalated"),
  ISBLANK(Reason_for_Escalating__c)
)

However, that formula won't work without modifying the API name used.  

Following the directions that were given, the Field Name automatically defaults to "ReasonforEscalating", which in turn creates "ReasonforEscalating__c" as the API name.  That means when you run the formula, the example listed won't work.  The API name needs to be manually set or the reference needs to be changed in the formula. 
 
Was something changed in the way Salesforce creates new field names after these modules were created?  I think that either the example formulas should be fixed or the instructions should be changed to show that you need to manually create the spacing to get the correct API name.  
 

I am completing MOBILE SDK NATIVE APP TRAILHEAD COURSE( https://trailhead.salesforce.com/modules/mobile_sdk_native_android/units/mobilesdk_android_getting_started)
but I'm getting stuck while building cloned repo using Android studio.

Error occured into build.graddle file: 
Error:(2, 0) Plugin with id 'com.github.dcendents.android-maven' not found.

First few lines of code are pasted below:

apply plugin: 'com.android.library'
apply plugin: 'com.github.dcendents.android-maven'
apply plugin: 'com.jfrog.bintray'

dependencies {
  compile project(':libs:SmartStore')
}

android {
  compileSdkVersion 25
  buildToolsVersion '23.0.1'

  buildTypes {
      debug {
         testCoverageEnabled = true
      }
  }

Please help me to resolve this issue.