Fix rspec fact tests

#555 introduced new
tests. In the same time we adjusted our test setup on the master branch
and #555 wasn't rebased before merging. This PR fixes the tests.

Author: bastelfreak

spec/unit/facter/pip_version_spec.rb

@@ -43,17 +43,15 @@
   describe 'pip2_version' do
     context 'returns pip2 version when pip2 present' do
       it do
-        Facter::Util::Resolution.stubs(:exec)
-        Facter::Util::Resolution.expects(:which).with('pip2').returns(true)
-        Facter::Util::Resolution.expects(:exec).with('pip2 --version 2>&1').returns(pip2_version_output)
+        allow(Facter::Util::Resolution).to receive(:which).with('pip2').and_return(true)
+        allow(Facter::Util::Resolution).to receive(:exec).with('pip2 --version 2>&1').and_return(pip2_version_output)
         expect(Facter.value(:pip2_version)).to eq('9.0.1')
       end
     end
 
     context 'returns nil when pip2 not present' do
       it do
-        Facter::Util::Resolution.stubs(:exec)
-        Facter::Util::Resolution.expects(:which).with('pip2').returns(false)
+        allow(Facter::Util::Resolution).to receive(:which).with('pip2').and_return(false)
         expect(Facter.value(:pip2_version)).to eq(nil)
       end
     end
@@ -62,17 +60,15 @@
   describe 'pip3_version' do
     context 'returns pip3 version when pip3 present' do
       it do
-        Facter::Util::Resolution.stubs(:exec)
-        Facter::Util::Resolution.expects(:which).with('pip3').returns(true)
-        Facter::Util::Resolution.expects(:exec).with('pip3 --version 2>&1').returns(pip3_version_output)
+        allow(Facter::Util::Resolution).to receive(:which).with('pip3').and_return(true)
+        allow(Facter::Util::Resolution).to receive(:exec).with('pip3 --version 2>&1').and_return(pip3_version_output)
         expect(Facter.value(:pip3_version)).to eq('18.1')
       end
     end
 
     context 'returns nil when pip3 not present' do
       it do
-        Facter::Util::Resolution.stubs(:exec)
-        Facter::Util::Resolution.expects(:which).with('pip3').returns(false)
+        allow(Facter::Util::Resolution).to receive(:which).with('pip3').and_return(false)
         expect(Facter.value(:pip3_version)).to eq(nil)
       end
     end