bump-version: remove sembump

- sembump (github.com/jessfraz/junk/sembump) is unsupported by
  the author and won't build on mac/windows. Make NEW_VERSION explicit.

Makefile

@@ -10,8 +10,6 @@ BRANCH ?= $(shell git rev-parse --abbrev-ref HEAD)
 LDFLAGS ?= -X github.com/digitalocean/csi-digitalocean/driver.version=${VERSION} -X github.com/digitalocean/csi-digitalocean/driver.commit=${COMMIT} -X github.com/digitalocean/csi-digitalocean/driver.gitTreeState=${GIT_TREE_STATE}
 PKG ?= github.com/digitalocean/csi-digitalocean/cmd/do-csi-plugin
 
-## Bump the version in the version file. Set BUMP to [ major | minor | patch ]
-BUMP := patch
 VERSION ?= $(shell cat VERSION)
 
 all: test
@@ -20,8 +18,8 @@ publish: compile build push clean
 
 .PHONY: bump-version
 bump-version: 
-	@go get -u github.com/jessfraz/junk/sembump # update sembump tool
-	$(eval NEW_VERSION = $(shell sembump --kind $(BUMP) $(VERSION)))
+	@[ "${NEW_VERSION}" ] || ( echo "NEW_VERSION must be set (ex. make NEW_VERSION=v1.x.x bump-version)"; exit 1 )
+	@(echo ${NEW_VERSION} | grep -E "^v") || ( echo "NEW_VERSION must be a semver ('v' prefix is required)"; exit 1 )
 	@echo "Bumping VERSION from $(VERSION) to $(NEW_VERSION)"
 	@echo $(NEW_VERSION) > VERSION
 	@cp deploy/kubernetes/releases/csi-digitalocean-${VERSION}.yaml deploy/kubernetes/releases/csi-digitalocean-${NEW_VERSION}.yaml

README.md

@@ -194,7 +194,7 @@ Dependencies are managed via [Go modules](https://github.com/golang/go/wiki/Modu
 To release a new version bump first the version:
 
 ```
-$ make bump-version
+$ make NEW_VERSION=v1.0.0 bump-version
 ```
 
 Make sure everything looks good. Create a new branch with all changes: