Don't allow float to end with a dot

lexer.go

diff --git a/lexer.go b/lexer.go
index c4a2bd6..0ad27a2 100644
--- a/lexer.go
+++ b/lexer.go
@@ -413,6 +413,12 @@
 	for {
 		next := l.next()
 		if next == '.' {
+			if point_seen {
+				return l.errorf("cannot have two dots in one float")
+			}
+			if !isDigit(l.peek()) {
+				return l.errorf("float cannot end with a dot")
+			}
 			point_seen = true
 		} else if isDigit(next) {
 			digit_seen = true

lexer_test.go

diff --git a/lexer_test.go b/lexer_test.go
index e5846bd..c2bb2f2 100644
--- a/lexer_test.go
+++ b/lexer_test.go
@@ -268,6 +268,22 @@
 	})
 }
 
+func TestFloatEndingWithDot(t *testing.T) {
+	testFlow(t, "foo = 42.", []token{
+		token{tokenKey, "foo"},
+		token{tokenEqual, "="},
+		token{tokenError, "float cannot end with a dot"},
+	})
+}
+
+func TestFloatWithTwoDots(t *testing.T) {
+	testFlow(t, "foo = 4.2.", []token{
+		token{tokenKey, "foo"},
+		token{tokenEqual, "="},
+		token{tokenError, "cannot have two dots in one float"},
+	})
+}
+
 func TestKeyEqualNumber(t *testing.T) {
 	testFlow(t, "foo = 42", []token{
 		token{tokenKey, "foo"},