Reference build dir to get correct sha

Author: jberkel

Tests/Carthage/.gitignore

@@ -1,2 +1,3 @@
 Carthage/
+Cartfile
 Cartfile.resolved

Tests/Carthage/Makefile

@@ -6,10 +6,13 @@ CARTHAGE_ARGS := --no-use-binaries
 CARTHAGE_TOOLCHAIN := com.apple.dt.toolchain.Swift_3_0
 CARTHAGE_CMDLINE := --configuration $(CARTHAGE_CONFIGURATION) --platform $(CARTHAGE_PLATFORM) --toolchain $(CARTHAGE_TOOLCHAIN) $(CARTHAGE_ARGS)
 TRAVIS_COMMIT ?= master
-TRAVIS_REPO_SLUG ?= stephencelis/SQLite.swift
+TRAVIS_BUILD_DIR ?= https://github.com/stephencelis/SQLite.swift.git
 
 test: $(CARTHAGE) Cartfile
 	$< bootstrap $(CARTHAGE_CMDLINE)
 
 Cartfile:
-	echo 'github "$(TRAVIS_REPO_SLUG)" "$(TRAVIS_COMMIT)"' > $@
+	echo 'git "$(TRAVIS_BUILD_DIR)" "$(TRAVIS_COMMIT)"' > $@
+
+clean:
+	@rm -f Cartfile Cartfile.resolved