Use correct build contraints (must be alphanumeric)

Fixes: https://github.com/golang-migrate/migrate/issues/52

Dockerfile

@@ -16,7 +16,7 @@ COPY database ./database
 COPY source ./source
 
 ENV DATABASES="postgres mysql redshift cassandra spanner cockroachdb clickhouse"
-ENV SOURCES="file go-bindata github aws-s3 google-cloud-storage"
+ENV SOURCES="file go_bindata github aws_s3 google_cloud_storage"
 
 RUN go build -a -o build/migrate.linux-386 -ldflags="-X main.Version=${VERSION}" -tags "$DATABASES $SOURCES" ./cli
 

Makefile

@@ -1,4 +1,4 @@
-SOURCE ?= file go-bindata github aws-s3 google-cloud-storage
+SOURCE ?= file go_bindata github aws_s3 google_cloud_storage
 DATABASE ?= postgres mysql redshift cassandra spanner cockroachdb clickhouse
 VERSION ?= $(shell git describe --tags 2>/dev/null | cut -c 2-)
 TEST_FLAGS ?=

cli/build_aws-s3.go

@@ -1,4 +1,4 @@
-// +build aws-s3
+// +build aws_s3
 
 package main
 

cli/build_go-bindata.go

@@ -1,4 +1,4 @@
-// +build go-bindata
+// +build go_bindata
 
 package main
 

cli/build_google-cloud-storage.go

@@ -1,4 +1,4 @@
-// +build google-cloud-storage
+// +build google_cloud_storage
 
 package main