Add makefile for bumping version number (#64)

Author: fractalwrench

CONTRIBUTING.md

@@ -59,7 +59,7 @@ Create a [Bintray](https://bintray.com) account:
 ### 3. Making a release
 
 1. Update the CHANGELOG.md file with any changes
-1. Bump the version number in `Notifier.java`
+1. Update the version number by running `make VERSION=[number] bump`
 1. Commit the changes
 1. Create a release build:
    * `./gradlew -Preleasing=true clean release`

Makefile

@@ -0,0 +1,10 @@
+bump:
+ifeq ($(VERSION),)
+	@$(error VERSION is not defined. Run with `make VERSION=number bump`)
+endif
+	@echo Bumping the version number to $(VERSION)
+	@sed -i '' "s/version=.*/version=$(VERSION)/" gradle.properties
+	@sed -i '' "s/NOTIFIER_VERSION = .*;/NOTIFIER_VERSION = \"$(VERSION)\";/"\
+	 src/main/java/com/bugsnag/Notifier.java
+
+