install: Rename variable referencing cmake version.

The next version is 3.0.0, not 2.8.13.

The version generated in the export file should be updated in
the release branch in both cmExportInstallFileGenerator and
cmExportBuildFileGenerator.

Source/cmExportInstallFileGenerator.cxx

@@ -114,7 +114,7 @@ bool cmExportInstallFileGenerator::GenerateMainFile(std::ostream& os)
   std::vector<std::string> missingTargets;
 
   bool require2_8_12 = false;
-  bool require2_8_13 = false;
+  bool require3_0_0 = false;
   // Create all the imported targets.
   for(std::vector<cmTargetExport*>::const_iterator
         tei = allTargets.begin();
@@ -160,7 +160,7 @@ bool cmExportInstallFileGenerator::GenerateMainFile(std::ostream& os)
       }
     if (te->GetType() == cmTarget::INTERFACE_LIBRARY)
       {
-      require2_8_13 = true;
+      require3_0_0 = true;
       }
     this->PopulateInterfaceProperty("INTERFACE_POSITION_INDEPENDENT_CODE",
                                   te, properties);
@@ -169,7 +169,7 @@ bool cmExportInstallFileGenerator::GenerateMainFile(std::ostream& os)
     this->GenerateInterfaceProperties(te, os, properties);
     }
 
-  if (require2_8_13)
+  if (require3_0_0)
     {
     this->GenerateRequiredCMakeVersion(os, "2.8.12.20131007");
     }