Use a separate Travis job for dependencies.

.travis.yml

@@ -12,6 +12,7 @@ env:
     # GitHub auth token (GH_AUTH_TOKEN)
     - secure: "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"
   matrix:
+   - BUILD_VERSION="prepare_dependencies"
    - BUILD_VERSION=""
    - BUILD_VERSION="disable_autoupdate"
    - BUILD_VERSION="disable_register_custom_scheme"

.travis/build.sh

@@ -84,6 +84,11 @@ build() {
   # Guideline Support Library
   getGSL
 
+  if [[ $BUILD_VERSION == *"prepare_dependencies"* ]]; then
+    success_msg "Dependencies were prepared successfully! :)"
+    exit 0
+  fi
+
   # Configure the build
   if [[ $BUILD_VERSION == *"disable_autoupdate"* ]]; then
     GYP_DEFINES+=",TDESKTOP_DISABLE_AUTOUPDATE"